Payment possibility to pay half

In the payment fields, the only thing that is required right now is the deposit upon submission. They only need to pay half of their total. Ie I want to be a vendor for 3 days ($75.00 and that is the actual cost) and I need an extra 6 Ft Table ($10.00 actual cost). So my total would be $85.00. The deposit would be half of what the total cost would be. So I need a way for them to only be able to pay half of what the total cost is, but they still need to see what the actual cost is. And I also need an option if they would like to just pay the whole thing at once. Is that possible? I would also like multiple examples.

You can achieve this by giving your users a coupon code:

http://www.jotform.com/help/233-How-To-Add-Coupon-Code-in-the-Payment-Form

You can also find this one very useful for you to accomplish your scenario:

http://www.jotform.com/help/225-How-To-Add-Options-In-The-Payment-Form