The Mazda MX5 (or Eunos Roadster) Mk 1 forms an excellent base for a budget trackday car. Fairly lightweight, reliable engine, rear wheel drive and neutral handling outweight the disadvantage of the underpowered engine. Not really suitable for the taller drivers, especially if you have a roll bar fitted, the cabin is not very large, but is ergonomically very well placed for the enthusiastic driver.
For less than £2500 you could have a track car setup with trick suspension, roll cage, uprated braking and sticky tyres, all perfect for annoying the faster kit. Predictable on the limit, they are the ideal introduction to Rear Wheel Drive. Working on them is very easy, with even a timing belt changing being suitable for novices. The entire suspension geometry is adjustable, with double wishbone suspension all round.
Imported cars tend to have less rust than UK cars, though obviously this depends very much on the way the car has been treated since entering the country (the Japanese do not salt their roads). Its a common myth that UK cars have more underseal than Jap spec cars; UK cars are the same as Japanese spec but with modifications to suit the UK market carried out in the UK prior to sale.