Add quantity in payment plugin

I would like an option to insert a product with a price at the backend. At the frontend this product and its price is displayed (single line, no dropbox or something like that) and there's also a field in front where you can add a number. So you can submit that you want 5 of those products for example. This way it would be easy to create a form where people could order my products in any amount.

So basically an order list.

5 Product A (€ 13,95)
3 Product B (€ 11,95)
10 Product C (€ 1,50)

Total € 120,60