£250 is about right. I pay similar for commercial ones. The only thing i would make sure is of the eletrics. The modern vehicles with caan bus electrics dont take kindly to 'scotch locks' (The plastic things reffered to above) being used or any other botching. Any spikes in the electric current or other such surges can inflict damage to the ecu of your vehicle or at best give you warning lights all over your dash due to it not communicating properly.
I get a thing called a multiplex wiring kit fitted to all of my installs which even though i am not mechanically/electrically minded to know what it does properly, i know it protects my vehicles electrics and maintains their warranties. Oh this is included in the price i usually pay.