Range from the cheapest cat flap installation £80 (J&K Expert Building Services based in EN5) to the dearest cat flap installation £200 (Absolutely 365 building based in N14).
Comparing carpenter & joiners estimates for installing a cat flap 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 fit a cat flap in EN4 by posting a job with HaMuch and we will send it to carpenter & joiners in EN4.