Emoney plugin gives your website its own virtual currency that will allow your users to earn and purchase using this built in internal currency.
Users can fund their Emoney wallet via Paypal, Stripe, Bank Transfer, (credits from Creditgifts Plugin if available) which be used to purchase within the website.
Emoney allow users to "cash out" their funds requiring you to pay their Emoney Balance on withdrawal.
Admin can set commission to take during each Widthdrawal/CashOut Request.
Managing internal currency system gives you complete control over monetization on your website.