Range from the cheapest replacement of a toilet float valve £25 (MJM Plumbing & Property Maintenance based in SW1V) to the dearest replacement of a float valve £80 (RD plumbing and heating services ltd based in SE15).
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 SE17 by posting a job with HaMuch and we will send it to plumbers in SE17.

"Replace float valve in toilet cistern as well as the other parts in the water tank. Rubber gasket (80mm) is old with limescale and disallows water from filling the tank."
SE1