I wouldn’t automatically dismiss a car due to previous repairs for rust. My Eunos had a advisory for sill corrosion but it was repaired at some expense by the MX5 Restorer. If you find one that’s been repaired by a reputable expert, or at least one with photographic evidence that the repair was completed properly, then why not?
I bought my latest MX-5 as a £500 punt two years ago. It hadn’t moved for seven years and I didn’t see it running before I agreed to buy. It went straight through its first MOT without any advisories. Phew!
During the past two years I’ve done brakes, cam belt etc. that you’d want to do to any car, but otherwise it’s cost me nothing. Not bad for a 24 year old car that’s kept outside and used as a daily driver.
Last year’s MOT had two rust advisories - rear subframe (minor) & sill/“seatbelt anchorage corrosion”. I’ve had second opinions and there’s just surface rust on the rear subframe - it’s a harsh advisory. The sill isn’t structural but the ‘crude’ (as Saz excellently put it) repair from 2010 has started to fail. As there’s nothing wrong structurally I’m planning on another ‘crude’ repair to keep it going relatively cheaply for another 2-3 years. The rear arches are starting to bubble too but I’m in no position financially to have a full sills & arches job done, especially considering what I paid for it, and the rest of the bodywork is only A3 (is that a thing?) rather than A1. Additionally, I’m of a mind that a bit of paint bubble can’t be seen whilst I’m enjoying the drive, but I know others feel differently. Maybe in the future I’ll be in a position to have it all done properly, but right now the few hundred a ‘crude’ repair will cost is worth it because structurally it’s good and the rest of the car is working beautifully. touch wood
My last MX-5 however was sadly rotten as a pear underneath and went to the great scrapyard in the sky. And years ago my second MX-5 looked great but the engine was knackered and the underside of it had an inch of crap on it that I found was covering up all manner of rust-related horrors. Both very different situations and I didn’t keep either.
You can find an MX-5 cheaply and spend ‘nothing’ on it for some time, even one that’s been repaired. Just depends on the repair and how perfect you want the car to look. There are some dogs out there, but I know of people who’ve been bitten by 5-year-old £20,000 dogs so age/price doesn’t necessarily come into it.
Good luck with your search. Go for it!