On its own, the SodaMod adapter is just shy of $60. They'll also sell you the properly sized refill paintball canister for your SodaStream compatible machine.
The giveaway here is for your very own SodaMod adapter. We're NOT giving away the SodaStream. If interested in the win, enter below. The giveaway is open through 11:59pm EDT on 5/31/15 to US entrants who are 18+. Void where prohibited.