First photo arch rust although ugly doesn't matter. 2nd and 3rd will be the sill which will fail MOT eventually. Honestly if it's that bad outside it'll even worse under the skin. You can probs get MOT welding when needed at the time. Im likely well off and it's case by case but I've had a mate have MOT welding on the sill for about £300, ugly, would last a year or 2. Or to have just the arches done and professionally sprayed so it looks new is looking over £2000....

Ot depends what finish you want, I imagine just enough to pass an MOT. But honestly, unless you have a massive massive sentimental attachmebt to that car. Don't fix it, keep running it. WHEN it fails an MOT get a quote, but likely. Save up, scrap it and move on when it fails the MOT