Adjust a Wordpress Plugin - Calculator

I am developing a Wordpress site and have installed the EZ Form Calculator, but unsure how to go about creating something similar to this; [login to view URL] I have all the details ready to go into the calculator. Here is how it should work (briefing). Once the person chooses how many editions they want (1, 3 or 6) - they choose an advert size from the drop down - so if they chose 1 edition it would add the advert price for just 1 issue, but it they chose 3 issues it would show the discounted price for 3 months (rather than the full price for just one month). Each adverts has 3 prices (1 issue, 3 issues, 6 issues) - To make it simple. 1. Choose how many issues you want to feature in 2. Choose the size of advert 3. Show advert price for the amount of issues chosen I also need this to connect to Paypal to allow the user to pay right then. Thanks