Range from the cheapest Fit a new plug socket £110 (Sam electrical based in Nw1) to the dearest Fit a new plug socket £210 (F&A Electrical based in W2).
Comparing electricians estimates for a Fit a new plug socket 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 by posting your job to fit a plug socket to electricians in NW3.