maybe some one wants to trade a gog game(10$ one) for terraria?
EDIT: This offer is long gone.
What AndrewC said, but also I'm trying to gather people to buy a 4-pack. I can do the buying since the UK has the cheapest price. At the UK price for a 4 pack (£17.99) it works out at ~£4.50/$7.27/€5.11 each. Let me know if you're interested.