About double what you think.
If you have the time, you should do all the prep work, so the hacking, clearing and so on.
Then only use the trade for putting new in.
Thats how I did it, although I did do a lot woodwork, tiling and plasterboarding myself.
I spent more renovating than i paid for the house itself.
It took me 2 years, working around 2 nights and one day per weekend per week on average, but it is a largish house and i hacked back to the stonework, replaced all floorboards, new insulation, ceelings, sand/cement/replasterand, new electrics, new plumbing, 3no staircases and so on. It probably would have been cheaper to new build, with getting the vat back.