A simple feature added, Add funds

Project please read.. I have a digital download site mand it's all setup and I have lots more products to setup, users can view invoices and downloads when they login. I simply want an add funds feature, so the user can add funds to there account and use those funds to buy anything on the site, the balance should be shown at the top of each members page with (add credit) link. In the admin part, I can edit profiles, I want add the ability to add credit or remove credit from any account and place a note on there, the credit would show up on the invoices page, where normal transactions are shown, and the reason for the credit or removal which will be displayed on the transactions page where the transaction normally is. Small budgets only, it should not be hard and take long, I also own a web hosting company, if you prefer to have an unlimited Alpha cpanel reseller account let me know, 3 years worth $2,400.