Forms plugin that works well with paypal?

I have formidable pro but it doesnt do what I want.

We have a fairly complex form, about 18 fields and about 4 of those fields will need pricing options depending on what people select. I need a forms solution that allows me to assign pricing to a field and have options with that field also, say theres 4 checkboxes in a field and each one ticked would add $10 to the price.

We dont want a plugin that has an annual fee, some looked great but the $150 PA or so isnt what my client wants. Im happy to pay for a pro plugin though.