Add discount in form plugin

Hello everyone.

I have a small problem. I am using gravity form now, and I want to write my prices but with disccount.

Example:

Producto 1: 20$, 1 unity
Product 2 : 10$ 1 unity:

When I show the final price. I want to show two prices. Like that:

Total: 30$
Discount: 5$
Total to pay: 25$

But with the plugin I just can show Total: 30$

Any ideas? I should use another form plugin?

Thanks!