$20 just about buys you a takeaway curry and a sixpack, so I think it's a fair price for the amount of game you've got in there. I reckon the average player's got at least 20 hours of play out of AF.
There's very strong anecdotal evidence that sales will decrease if I lower the price.
There's also very strong anecdotal evidence that if people actually want something they'll buy it if it's even at a halfway reasonable price at all. I couldn't get away with $40 but any way you look at it $20 just isn't much for something you can enjoy playing for a few weeks. So that's one thing I definitely can't change.
An Instant Buy option would be excellent but I haven't quite figured out the mechanics of this yet. I'd need to SSL to my server and forward the request in realtime to some payment processing net service, and that's where it starts getting complicated because there's all sorts of pesky ways for it to break which I'll get wrong for the first few cuts.
I think the next big thing I'm going to put in is a feedback form on the demo to ask people things about the game like whether they think it's worth $20 or whether it's too hard or crap or whatever.