I had mine done by a company based in Milton Keynes call Pristine Alloys, they were the company that were contracted by Lexus to do all the warranty repair work so the work is top notch.
I think it was about £60 a wheel with the diamond cut faces, but that was on a wheel exchange program so would be a bit cheaper for bare wheels.
Or theres BJV Engineering in Hemel Hempstead, their prices are the best I've seen (£160 for a set of 4 with diamond cut faces). But cant comment on the quality of their work, although I'm planning on getting them to do mine in the next week or so.