the cheaper prices that people are quoting on here are for generic maps, eg a map that has already been made up on a previous car. Needs flashing onto the ecu. thats very easy and for the person that uploads them to the ecu, its free! But its the initial outlay to get that map that you pay for, which to be honest, is paid for with the first few sales!
Those who have been quoted £450-and over that will be a custom remap on a rolling road specific to your car, you pay for rolling road time, fuel used, labour etc so costs are higher but generally speaking results will be better too.
No cars engine is the same. to a generic map may be great for one car say 10bhp gain, and on another car with same engine, may only produce 7bhp gain!
thats why you have a custom map done.
On my saxo (supercharged) my car spent near 3 days on the rollers gettin it perfected. cost me a lot! but well worth it. Thats an extreme case though, a typical remap would take best part of a day to get right.