ecommerce catalog with credits instead of purchases

Hi, I’m looking to set up an ecommerce site with a product catalog, but instead of users purchasing items with dollars I need to pre-credit them with chits or ‘dollars’ and instead of them proceeding through a full ecom cart, the purchase happens internally.

1. User is credited with 100 ‘credits or dollars’.
2. User browses site and chooses products up to that amount.
3. On cart completion admin is send a purchase order to fulfill those products.
4. No actual money is exchanged.
5. I also need inventory tracking.

Sidenote: The admin will actually be doing all the transactions for the users, but I will still need to be able to track each individual user’s fake purchases.

Any ideas on hacking woo-commerce or another shop plugin to get this done? One idea I had was to just set up a full woo-commerce shop with paypal and hook it up to sandbox. Just process all transactions as I would normally but sandbox removes the actual need to transact real dollars.