A friend of mine at work has started doing remaps, hes based in s/e kent but his brother lives in hertfordshire i believe and also does the same.
Its the generic mobile maps they do, but you tell em what you want and they sort you out, wether it be economy or power or anything inbetween. They even do anti-lag and launch control!!
I think prices start at around £150, which at that price i dont think you can go wrong with.
My mates doing mine for me friday, and ive only heard good reviews off other peoples hes done.
Hes got a facebook page called "kent vehicle remapping" send him a message and see what he says