If you'd like to get a cheap copy of The Moon Sliver, go get yourself a copy of The Groupees Community Bundle 3. You can pay anything upwards of $1, and choose to donate part of your payment to Juju, a young boy who is recovering from a terrible accident.
Besides The Moon Sliver, the Community Bundle also includes several other games (including another one of mine called Down We Go), as well as comics, albums, and ebooks.
Note that if The Moon Sliver makes it onto Steam, bundle purchasers will receive a free Steam key for the game.