Range from the cheapest Fit a radiator £100 (Naim Brace based in N9) to the dearest Fit a radiator £220 (Citywide plumbing&heating based in N18).
Comparing heating engineers estimates for fitting a new radiator in Upper Edmonton gives you an idea of who will be better value, but the best way to compare costs is to get actual quotes. Radiators vary in price, and additional hours will be required to make pipework changes.
What to do - Get rates and quotes for removing your old radiator and replacing it with a new radiator by posting your job to heating engineers in Upper Edmonton.

"Fit 7 flat radiators"
E4
"I would like to get a quote for moving two radiators in the living room from horizontal to vertical. We would need recommendation on the size of the vertical radiators to buy as well."
E17