Range from the cheapest replacement of a toilet float valve £25 (Secured PHO based in NW10) to the dearest replacement of a float valve £65 (Four Seasons based in NW6).
Comparing plumbers estimates for replacing a toilet float valve in the cistern tank gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - Get rates and quotes to replace a toilet float valve in NW2 by posting a job with HaMuch and we will send it to plumbers in NW2.

"My toilet makes a horn noise after flushing. I have the valve, but I was unable to replace it myself, because flushing only empties half of the cistern. So that may also need looked into. "
NW6