I grabbed the mayhem bundle (with killzone 3 and resistance 3) awhile back and have been having fun playing through Killzone with the sharpshooter. It takes some getting used to but it's a pretty fun and unique way to play a shooter.

It actually feels a bit more natural than a controller for me since I'm coming from playing fps games mainly on the PC. For under 100 I'd say this is a pretty good way to try it out.