Range from the cheapest single storey extension £47,000 (Eco Future Build based in BR6) to the dearest single storey extension £55,000 (Silverland design & build based in BR1).
Comparing extension builders estimates for fitting a downstairs toilet 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 build a single storey extension in Orpington by posting a job with HaMuch and we will send it to extension builders in Orpington.

"Single storey extension"
BR2