What game should I buy for 20 dollars or lower?

READ THIS FIRST: (I don't want people to recommend me games I already own)
These are the games I own:
Driver San Francisco
East India Company Gold
Enclave
FlatOut
FlatOut 2
Garry's Mod
Glacier 3: The Meltdown
Grand Theft Auto IV
One Finger Death Punch
Orborun
R.US.E
Race The Sun
Star Wars - Battlefront II
Steel & Steam: Episode 1
Take On Helicopters
Terraria
Yet Another Zombie Defense
Don't recommend games that require a really good PC, like GTA V or something.

Added (1). I already have Steam, I Already have Minecraft.-…
And Grid 2 isn't under 20 dollars. It's 30 dollars.

Minecraft? Your PC doesn't have to be a supercomputer for that.

Grid 2 Game! What game should I buy for 20 dollars or lower - 1

Well, some good news for you i guess:
Simply download Steam. The most awesome free games on Steam include Dota 2, Team Fortress 2, Warframe, APB Reloaded, Unturned and many many more. Plus lots of discounts on paid games so yeah, I'd recommend Steam.