Telco Plan Builder - How to?

Hi All

I want to create a form that provides a calculated monthly cost after you the choose parts of the plan you like. In this instance, you have your broadband speed selections, then your monthly data quota, then your additional speed boost, and then also phone. As you click through these options, i want an equation to calculate a total so that it can A/ be displayed on screen as they vary their choice, and B/ retain as the quoted monthly figure at the end which they can sign up to.

Would love to hear some thoughts. I get the feeling there may be several ways to skin this cat, of which any will take me some time to nut out, so a heads up might be a good start :)