Agreed that a payment investment which is reduced from the price of a full game would limit the potential losses to any one consumer, and is a good idea.
If 10,000 people like your idea and the assets you've come up with so far well enough to give, say, $20 each, that's $200,000 to play with, which isn't too bad a budget for an indie game. I think that's a very achievable goal - the idea would have to be innovative and enticing, the development process would have to be open enough that people see their money is being put to good use (I'm not saying to give the consumers any real power over the game, but a blog with semi-regular screenshot posts would keep people assured that it's not abandonware), and you'd have to pump a little bit of your own money into it at the start to get those initial assets looking good... if you can do that then I would imagine that the community support would come through for you.
I'd see the "payback" on your investment being a copy of the game at the end, as well as beta access etc if applicable. If all goes to plan you'd be getting a good deal as one of those 10,000 investors; you'd have paid $20 for a $40 game, perhaps.
Hopefully real time weapon change will make up for it.