I really enjoyed playing Dead Nation with my flat mate, but that's on the PS3 network and I don't know whether it is that cheap. I heartily reccomend that.
Also there's some stuff on GoG that's going pretty cheap. If you don't mind playing an older game then I'd reccomend Hostile Waters. It's a sort of remake of carrier command with an incredibly simple and intuitive control function that was remarkably ahead of its time as well as incorporating great action elements and resource management. It's also narrated by that bloke what was the best doctor who. The one with the big scarf.
Also there's some stuff on GoG that's going pretty cheap. If you don't mind playing an older game then I'd reccomend Hostile Waters. It's a sort of remake of carrier command with an incredibly simple and intuitive control function that was remarkably ahead of its time as well as incorporating great action elements and resource management. It's also narrated by that bloke what was the best doctor who. The one with the big scarf.