Aliens: Colonial Marines | Currys eBay Outlet | £1.97
PC price comparison | Aliens: Colonial Marines Review
Yes, Colonial Marines is a big bag of xenomorph effluence. But sometimes a bad game can be worth dropping two quid on just for the lulz. Alternatively, you can probably buy the DVD of Aliens for this much. Or a little paint tester kit, which you could watch dry.
The disc also makes a great coaster. Thanks to Irah @ HUKD!