Range from the cheapest Downlights installation £290 (SR Gas and Electricity LTDG Ltd based in KT5) to the dearest Downlights installation £440 (Wired Get Connected based in TW11).
Comparing electricians estimates for Downlights installation 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 for installing downlights by posting a job to electricians in KT1.