diff -u b/modules/recurring_events_registration/recurring_events_registration.views.inc b/modules/recurring_events_registration/recurring_events_registration.views.inc
--- b/modules/recurring_events_registration/recurring_events_registration.views.inc
+++ b/modules/recurring_events_registration/recurring_events_registration.views.inc
@@ -37,6 +37,13 @@
       'field' => 'event_registration__capacity',
       'id' => 'eventinstance_registration_availability_count',
     ],
+    'argument' => [
+      'title' => t('Registration Availability Count'),
+      'help' => t('The number of registration spaces available for an event instance.'),
+      'field' => 'event_registration__capacity',
+      'id' => 'eventinstance_registration_availability_count',
+      'filter' => 'intval',
+    ],
   ];
 
   $data['eventinstance_field_data']['capacity'] = [
diff -u b/modules/recurring_events_registration/src/Plugin/views/filter/EventInstanceRegistrationAvailabilityCount.php b/modules/recurring_events_registration/src/Plugin/views/filter/EventInstanceRegistrationAvailabilityCount.php
--- b/modules/recurring_events_registration/src/Plugin/views/filter/EventInstanceRegistrationAvailabilityCount.php
+++ b/modules/recurring_events_registration/src/Plugin/views/filter/EventInstanceRegistrationAvailabilityCount.php
@@ -2,8 +2,6 @@
 
 namespace Drupal\recurring_events_registration\Plugin\views\filter;
 
-use Drupal\Component\Utility\Xss;
-use Drupal\Core\Form\FormStateInterface;
 use Drupal\views\Plugin\views\filter\NumericFilter;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\recurring_events_registration\RegistrationCreationService;
@@ -58,31 +56,6 @@
   /**
    * {@inheritdoc}
    */
-  public function operators() {
-    $operators = parent::operators();
-    // Offer limited operators.
-    return array_intersect_key($operators, array_flip([
-      '>',
-      '<',
-      '=',
-      '!=',
-      '<=',
-      '>=',
-    ]));
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function valueForm(&$form, FormStateInterface $form_state) {
-    parent::valueForm($form, $form_state);
-    unset ($form['value']['min']);
-    unset ($form['value']['max']);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function query() {
     // Set -1 as the default value so that if no events match the checks, then
     // we should get no results, rather than all results.
@@ -95,7 +68,7 @@
     // Remove any instances of this filter from the filters.
     if (!empty($filters)) {
       foreach ($filters as $key => $filter) {
-        if ($filter instanceof EventInstanceRegistrationAvailability) {
+        if ($filter instanceof EventInstanceRegistrationAvailabilityCount) {
           unset($view->filter[$key]);
         }
       }
@@ -107,20 +80,55 @@
     $view->preExecute();
     $view->execute();
 
-    $value = $this->value;
-    error_log(print_r($value, TRUE));
-    return;
-    $value = Xss::filter($value);
-
-    $operator = $this->operator;
+    $value = $this->value['value'] ?? NULL;
+    $min = $this->value['min'] ?? NULL;
+    $max = $this->value['max'] ?? NULL;
 
     if (!empty($view->result)) {
+      // Loop through results, evaluate result's availability re: filter settings.
       foreach ($view->result as $key => $result) {
         $this->registrationCreationService->setEventInstance($result->_entity);
         $availability = $this->registrationCreationService->retrieveAvailability();
 
-        error_log("$availability $operator $value");
-        if (eval("return $availability $operator $value")) {
+        $filter_result = FALSE;
+
+        switch ($this->operator) {
+          case '<':
+            $filter_result = $availability < $value;
+            break;
+          case '<=':
+            $filter_result = $availability <= $value;
+            break;
+          case '=':
+            $filter_result = $availability == $value;
+            break;
+          case '!=':
+            $filter_result = $availability != $value;
+            break;
+          case '>=':
+            $filter_result = $availability >= $value;
+            break;
+          case '>':
+            $filter_result = $availability > $value;
+            break;
+          case 'between':
+            $filter_result = $min <= $availability && $availability <= $max;
+            break;
+          case 'not between':
+            $filter_result = !($min <= $availability && $availability <= $max);
+            break;
+          case 'regular_expression':
+            $filter_result = preg_match($value, $availability);
+            break;
+          case 'empty':
+            $filter_result = !$availability;
+            break;
+          case 'not empty':
+            $filter_result = !!$availability;
+            break;
+        }
+
+        if ($filter_result) {
           $items[] = $result->_entity->id();
         }
       }
only in patch2:
unchanged:
--- /dev/null
+++ b/modules/recurring_events_registration/config/schema/recurring_events_registration.views.schema.yml
@@ -0,0 +1,8 @@
+views.filter.eventinstance_registration_availability_count:
+  type: views.filter.numeric
+
+views.filter_value.eventinstance_registration_availability_count:
+  type: views.filter_value.numeric
+
+views.argument.eventinstance_registration_availability_count:
+  type: views.argument.numeric
only in patch2:
unchanged:
--- /dev/null
+++ b/modules/recurring_events_registration/src/Plugin/views/argument/EventInstanceRegistrationAvailabilityCount.php
@@ -0,0 +1,119 @@
+<?php
+
+namespace Drupal\recurring_events_registration\Plugin\views\argument;
+
+use Drupal\recurring_events_registration\RegistrationCreationService;
+use Drupal\views\Plugin\views\argument\NumericArgument;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Argument handler to accept an availability count.
+ *
+ * @ViewsArgument("eventinstance_registration_availability_count")
+ */
+class EventInstanceRegistrationAvailabilityCount extends NumericArgument {
+
+  /**
+   * The registration creation service.
+   *
+   * @var \Drupal\recurring_events_registration\RegistrationCreationService
+   */
+  protected $registrationCreationService;
+
+  /**
+   * Constructs a new EventInstanceRegistrationAvailability object.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\recurring_events_registration\RegistrationCreationService $registration_creation_service
+   *   The registration creation service.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, RegistrationCreationService $registration_creation_service) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->registrationCreationService = $registration_creation_service;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('recurring_events_registration.creation_service')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query($group_by = FALSE) {
+    // Set -1 as the default value so that if no events match the checks, then
+    // we should get no results, rather than all results.
+    $items = ['-1'];
+    $table = $this->ensureMyTable();
+
+    // Grab the current view being executed.
+    $view = clone $this->query->view;
+    $filters = $view->argument;
+    // Remove any instances of this filter from the filters.
+    if (!empty($filters)) {
+      foreach ($filters as $key => $filter) {
+        if ($filter instanceof \Drupal\recurring_events_registration\Plugin\views\argument\EventInstanceRegistrationAvailabilityCount) {
+          unset($view->argument[$key]);
+        }
+      }
+    }
+    // Execute the current view with the filters removed, so we can reduce the
+    // number of event instances we need to examine to find their availability.
+    // This makes the query more efficient and avoids having to do messy union
+    // selects across multiple tables to determine the availability of an event.
+    $view->preExecute();
+    $view->execute();
+
+    if (!empty($this->options['break_phrase'])) {
+      $break = static::breakString($this->argument, FALSE);
+      $this->value = $break->value;
+      $this->operator = $break->operator;
+    } else {
+      $this->value = [$this->argument];
+    }
+
+    if (!empty($view->result)) {
+      // Loop through results, evaluate result's availability re: filter settings.
+      foreach ($view->result as $key => $result) {
+        $this->registrationCreationService->setEventInstance($result->_entity);
+        $availability = $this->registrationCreationService->retrieveAvailability();
+
+        $filter_result = FALSE;
+
+        if (count($this->value) > 1) {
+          $filter_result = array_search($availability, $this->value) !== FALSE;
+        }
+        else {
+          $filter_result = $availability == $this->argument;
+        }
+
+        if (!empty($this->options['not'])) {
+          $filter_result = !$filter_result;
+        }
+
+        if ($filter_result) {
+          $items[] = $result->_entity->id();
+        }
+      }
+    }
+
+    // Filter this view by the events which match the availability above.
+    $items = implode(',', $items);
+    $this->query->addWhereExpression(0, "$table.id IN (" . $items . ")");
+  }
+
+}