The dream car can turn into a nightmare. An increasingly high percentage of Mk1s now at the sub-£1000 mark are probably approaching basket cases, where the rust is more than sheet metal needing welding, bt more expensive parts needing full replacement. Less rusty cars can be found, but that’s mostly cars being sold by people who don’t understand the value; the last place to find those owners is an Owners Club forum.
If the dream is based on driving manners, consider extending the search to include the Mk2 (NB). Plenty of roadworthy examples for under £1000 (sub £1000 Mk1s likely to be MOT-less, and will need to be trailered, which might add significant cost). Plenty of those won’t be basket cases. Yes, they need rear sills, rear arches, front chassis rails, but you are less likely to find rotten floor pans, bulkheads, A-pillers. They drive just like a Mk1 (under the panels, they are basically identifical). Early Mk2s in a solid colour I can see getting to a classic status.
Surprised a base MGF costs more to insure than a MX5. Most of the cheap surviving Mk1s worth looking at are JDM imports, and once you declare that, the insurance cost doubles. You can SORN a car. Just because it has a MOT, doesn’t mean you are obliged to re-MOT or tax it.
As for taking said basket case when you are worried about the cost of a MOT, to tracks “around the world”, thats a bit deluded to say the least.