Hi! 
My partner and I are buying our very first home in Walthamstow. Of course, I like to make life difficult, so instead of being sensible and getting a home in good condition to start off with (maybe a lick of paint and new carpets, no biggie, I can do this, kinda place) I had to get a house that looks like it took style inspiration from an old age home. Not a big deal (if you ignore the shower chair), however it is TINY. So of course, I decided that I was just going to renovate the whole thing and build out a double-story rear extension to house a new kitchen and bathroom. Because why the hell not?! 
We've been given building plans from the previous owners, which have been approved by the council. Because the house is so narrow, there isn't that much of an extension to be built on - it's an L-shape that extends out by 3m and is 3.48m at its widest point.
I have £55000 to complete the work which I thought was enough, however, when browsing through Houzz last night, I saw companies listing work they'd done with a price bucket of £75,000 - £100,000!!! So now I'm in the middle of a mental breakdown, wondering whether I should pull out of the sale because I can't afford to do anything.
I would love to know what other people's experiences have been with house extensions in East London. Has it really been as expensive as this? Any advice, thoughts, recommendations would be so very much appreciated xxx