Calculation Based On Check Boxes

[mginipro]

I'm reorganizing a database and would like to set up a calculation which returns a "Balance Due" based on a check box value list. Currently, it works perfectly when only one of the check boxes is selected, but I can't get the correct calculation to work when two or more boxes are checked. Here's what I have:

If(Session = "Camp1", 100, If(Session = "Camp2", 325, If(Session = "Camp3", 510,0)))

So, if someone is coming to Camp1 the result is $100 and so on. If someone decides to come to Camp1 and Camp2, I'd like a result of $425, but the ways I've tried to set that up have all resulted in giving me a result of 0.

I know I can simply add "Camp1 & Camp2" to my value list and then to the calculation, but I've got to imagine that there is a way to be able to add two or more values in the calculation.

Thanks in advance for any help!

[Robert Kidd]

Try:-

Case(PatternCount(Session,"Camp1"), 100)+

Case(PatternCount(Session,"Camp2"), 325)+....