Taxonomy Enhancer is a module which will extend the fields available to any given term. Each Vocabulary is fully configurable in its own right and can have as many fields "bolted on" as one likes.
Unfortunately (or fortunately, depending on how you wish to look at it), Drupal does not provide a "term load" or "vocabulary load" hook. There are hooks to pick up when a term or vocabulary is inserted, updated or deleted - but not loaded. This means that this module cannot easily pickup and extend a term automatically. This causes Taxonomy Enhancer to be more of an "on demand" service which is a double edged sword. On one hand, you are not bloating terms unnecessarily - you may not ALWAYS want the term to be extended. On the down side, it does mean that you will have to manually invoke the extension of the term when you need it.
This module defines the "money" field. It uses the Currency API, which is included in the Currency module, to get a list of existing currencies and their symbols.
The form element for amount is reused from the Formatted Number CCK module. Decimal points and thousands separators are formatted using the Format Number API module, where these options are configured from site and/or user settings.
The currency conversion dialog submodule requires jQuery 1.3.x (jQuery Update 6.x-2.x) and jQuery UI 1.7+ to work properly.
You may also want to check out Measured Value Field, which is pretty similar to Money field, but allows you to combine numeric fields with other units of measurement.