Nelly - thanks for the advice. I wasn't expecting it to be much more than £200, but if you say £315 isn't necessarily too much, I'll go with that.
Andyb -
Oh my aching sides! :P
Yeti - thanks for the offer, mate. I'll grill the local firm I'm thinking of using and if he doesn't inspire me with confidence, I may well take you up. Cheers.