Adding to a calculated sum based on a radio button selection

I'm brand new to Acrobat forms calculations.  I consulted a couple of JavaScript programmers, but they're flummoxed by Adobe's field properties!

I have an order form where the user can request up to five products - each resulting in a simple calculation of qty * cost.

There's an additional radio button selection for a website in one of two options. If either choice is selected, I need to add the cost of the website to the total of the five other products.

Help!   And thanks!