From my client, geminicourses (www.geminicourses.com)

At the same time, could you also look into the idea we mentioned before about the high season supplements? I am starting to add all the 2010 dates and fees at the moment and would like this facility in place for 2010 if poss. What it usually involves is a fee that applies from a certain date until a certain date and that would need to be added to the total price. It would need to be applied to course and / or accommodation. For example, a school may have a fee of £30 per week on the course between 1st July - 30th Sep. Another may have a fee of £30 per week on accommodation from 15th June - 15th Sep etc etc.

This may already be possible using conditional actions, but needs investigation.