One thing is, it sounds like it’s entirely garage-maintained? That changes the bangernomics a bit. It makes a big difference if you can do the donkey work, brakes and that. (and a huge difference if you can do bigger jobs, mine’d probably have gone in the bin if I’d had to pay garage prices for the new turbo)
What does your mechanic think? Well, presumably he thinks you should give him £800, but is he giving you a stack of advisories, or muttering about the rust in the sills that’ll want welding soon, or anything like that? Chatter is good, always worth trying to engage the mechanic in a bit of conversation.
(my brother’s sneaky, he’ll raise invented concerns with the place that does his van, to see what they say “It’s really rattly” got “well, it’s a sheddy van, it’ll rattle” not “we will spend £1000 on fixing rattles” or “That’s probably because the doors are falling off”.)