simulator

Do you have access to SPSS?

However, If you want to do affordable modeling quickly then why not start by using R http://www.r-project.org/ I would us this to get the logic right, its exceptionally quick to use and plot graphs etc. Then for the bank you'll have to hard code your work in C++ and produce a nice interface. Getting the numerics right is usually the hard part.

I'd be interested to read more about your simulator and how you propose it'll work. I'd a lot of experience with modeling risk for insurance etc, and its probably on a similar thread. Presumably you've taken measurements or you have some other external predictor of customer numbers?