Looking at the rust in the engine bay on the bulkhead and the rear chassis member I would budget at least for a bulkhead replacement and inner wings so £22,000 tops.
The level of corrosion viewable in the engine bay area is disturbing and suggests it's been subject to a marine environment to me or lived outside under a cover.
It's in an auction for a reason....I wouldn't touch it with a barge pole tbh when there are some really good examples around right now about the 30k mark.
A bit like our house when we bought it: "It took longer than I thought it would and eventually cost more than we had".