Range from the cheapest Downlights installation £240 (Elmark Ltd based in SE20) to the dearest Downlights installation £440 (J Durka Electrical based in SE26).
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 SE21.