Merlin are an LBS if you happen to be in Chorley, albeit with a large web presence
Spa, also an LBS, have a large range of handbuilt wheels
The cost will very much depend on the parts you use. The parts for my handbuilts cost around £200 with savvy shopping IIRC (mavic open pro rims, DT Swiss spokes (32/36), Novatech hubs)