If you're thinking about extending then that would have to be done first. And when you do that I suspect the house will need rewiring (I can't see many sockets on the pictures, and given the general condition it will probably need doing.) Possibly would need to redo the plumbing as well.
For an 8mx4m extension I think people are normally looking at about £2k per square metre in that area, so £60k+. But this is for up to first fix only, and wouldn't include your kitchen, new bathroom (if that's really urgent), and rewiring/replumbing, which could altogether add another £30-50k+.
It is possible to do it cheaper if you know what you're doing, and have good trade contacts, but don't assume that you could.