Not sure if this is cheap or not (also, this is EU/UK only) but TO ME this seems pretty cheap (as long as you have room on your ps3)

Bioshock Game (Code by Email) PS3 - nzgameshop.com

Once you order they just email the code (only during business hours)
Only $8 NZD, which is what...5 pounds? $6-7 USD? lol

Edit: I cant confirm whether you have to have a new zealand address or not, I don't think you do especially considering nzgameshop is based in the UK.