Ecommerce Site with Variable Pricing Per User

I am building a website where a registered user with a role of "salesman" can go out and sell different packages to people. There are 3 packages, A, B, and C. I want to be able to fix a minimum price for these values, but each "salesman" can raise the price for each to make a better commission. After a package gets added to the cart, a regular checkout process via credit card happens. Can anyone offer suggestions on how to tackle this?