I built this DIY canister filter out of an Otterbox.
DIY Canister Filter For A Nano Tank
It's been running for over a year now with no problems what so ever. I'm very happy with it but I don't think it meets your criteria of cheap...or easy.
Even if you had all the supplies laying around, the otter box will set you back about $30 with shipping, (you might be able to find it cheaper on sale somewhere, but I wasn't) and at that point it is cheaper to purchase a nano canister.
The good thing about this is you can customize it. You could add an in canister heater, if you bought the largest otter box and bought one of the small, flat, betta bowl heaters.
You might not want to buy the otter box (I would really recommend it though for it's water-proof properties) but you can at least get an idea of the required steps based on the tutorial and you-tube videos and go from there.