I need a resource for building some complex math functions

I need a resource for building some complex math functions within a Word Press site. I have a client that I want to program a job quoting system. So sales can log on and get to an input page that they give the job parameters. The system needs to then calculate several functions, lookup a couple of items and then calculate a quoted price that sales can give to a customer.

Right now I am looking for some resources so I can start reading up on the programing.

Any ideas?