[adamr8965]

You can gain more mpg without remapping the car.
You can lift off the throttle early when slowing down, Accelerate gentle and keep the revs low.
Block changing of the gears.
Correct tyres pressures, Clean oil in the engine, Sit at 50mph rather than 60mph.

Do all those and you'll be suprised how much your mpg will improve by, plus you have saved yourself around £450 for a decent remap.