I think you just scratched the potential of making some money out of your game. It is still Episode I, so you can offer on Episode II something that only paying custumers will get, like: a One-time Redeem Code given after purchase that they can register into their steam account to receive in game an item, just as an idea. Other things that are quite usual and I think ppl should explore is the ability to maintain an item market inside the game (once you get enough content for ppl to explore it) that they can use ingame and only way to obtain it is paying. The last solution would make you put the game for free and the money earned by the market would more than pay for the development in the long run.
Keep up the good work, dont give up on your project. I also agree 100% with all the previous posts and Im sure my two cents might help aswell.
Cheers!