Combining a form with a checkout method

Right now I have a Ninja Form that does everything I want except allow the ability for a user to select a couple options via radio button/checkboxes and then make a credit card payment. I’ve combined what I want by using eShop.

See> http://www.bgtb001.info/shop/kid-fest-vendor-prepay/

Once the application has been filled out and submitted they now have to remember to use the bottom of the page to select their item and pay for it. I need to merge the functions of Ninja Forms and eShop together.

I want to merge the two. I want the ability for them to fill out the application and it’s also a payment page as well, allowing them to kill two birds with one stone.

What plugin can do that and at the most affordable price?

Thanks all!!