Unlike others, I don’t think any conclusons can be drawn from one photograph of a rusty arch. Its rusty, but I’ve seen worse.
Would have been more useful to look more at the front; the footwells. It was always a given that rear sills, arches were needed.
Mototpunk had an article on a similarly aged UK spec car
One side of my MX5 (never had rust on the MOT records) went from this
Both sides done.
If you can weld, it doesn’t cost you that much to repair, just time.
Its naive to think a £500 31 year old to be rust free, and not needing significant repair.
Ok, so the rear sills and arches are shot. Not unexpected. Wheat did the front wings look like? Lift up the carpets, how did it look? Underneath; garage says “rotton”; is that proper holes everywhere, or just crusty looking subframes. The floor pan c-channels, solid or not (if rotted, an easy fix); check at the ends. Engine bay; you say it was rusty, was there actual rust (check under the wings). On the plus for this car; its been stored on a wood floor, which I assume is raised off the ground.
The goalposts as to whether this car is financially worth repairing (ie. paying someone else) is constantly moving. The idea that, for instance, someone would ask £5k for a car with a patched sill and needing further external cosmetics, would have been given short shrift a year ago. Now, I’m not sure. There is significant price inflation going on. Pre-“situation”, Hagarty had the Mk1 down as 8% CAGR. I suspect its doubled now.
If the only significant rot on that red car was the arches and sills, then it was more of a bargain tha n one that is £1500, with P38 stuffed (or worse) sills (because the repair costs are the same whether you’ve paid £500 or £1500). But I really don’t have any idea based on one photo.
My 1996; never an advisory or fail for rust. But nevertheless, both rear arches and sills needed to be replaced.
Ignore that MOT trail, actually look at the car. Its 31 years old. Its going to be rusty (otherwise, give up now looking for a NA). Otherwise you are wasting the sellers time. Could have gone to see that, made some sucking noises, muttered some “worse than I thought” while making crunching noises. When going to see stored cars like this, take with you a spare battery, to see if the engine turns over at all.