(Disclosure: This site contains product affiliate links. We may receive a commission if you make a purchase after clicking on one of these links. Read our affiliate disclosure for more info.)
IndieGameStand has a pay what you want deal for 99 Levels To Hell.
Minimum price is $0.25. Pay $1+ for a Desura and a GOG activation key. Note that the GOG key expires on 12/1/13.