You could save yourself a lot of trouble and instantly take advantage of a large number of assets by using Ripple as the back end of your exchange. Use gatewayd (intro video) as the gateway infrastructure to link the game's servers into Ripple's decentralized exchange and your users can trade IRI against any of the other assets currently traded on Ripple.

Your game client code could present a curated selection of trade pairs within the game, but users would also have the option to trade against the full range of cryptos, fiat and physical vaulted bullion using the Ripple client of their choice. This will give IRI better liquidity than if it is only traded by players within the game.

Long before you go live, offer autobridging will be deployed, so IRI should enjoy liquidity to all manner of assets without additional effort on your part. Think about it.