I know it's still a little early (in the Alpha) for a pre-purchase option, or even a Steam "early access" that companies so often do, allowing those who purchase their games early to participate in the unfinished process, but having said that, I think this game has attracted so much attention people would be willing to pay for it even without getting early access.
I know this game has had a much longer gestation period than you guys anticipated, and so many of us are SUPER EXCITED for it to be released. I wish we had a way to help you monetarily while you finish things up, and also have the peace of mind knowing that we'll be able to play the game the second it comes out.
Please consider it!