Could someone give me a heads-up as to the cost of a plumber to replace a thermostatic cartridge in a Bristan mixer bar shower. I have the cartridge, so the cost would be labour only. I live in Norfolk, so not London prices. I had a guy come round this morning quoting me £75 - this seems expensive. Bristan themselves told me that it would take around 15-20 mins max to replace the cartridge. Please advise. Many thanks.