Parcel Farce International was always the cheapest when i ran the dispatch dept a while back. They were the slowest and most unreliable though!
Just make sure that what your shipping isnt a restricted import. We sent a £2000 radio receiver to the US and it was impounded by US customs becasue it received the cell phone bands which is very illegal over there. The odd thing was that the radio eventually arrived back at our shop (three months later) and the buyer never complained or asked for his money back!!