MX-5s are the way to go. Got mine for £900, strip it out and add seat £120, harness £50, and roll bar £200, and you're there. Anything else is just adding performance if you want to, but for sub-£1500 you've got a perfect trackday car that's incredibly cheap to run as it's so light. No point in track insurance for something that cheap, just consider it expendable. Even if you wrote it off you'd be able to salvage something to use in the next one, and if you can't then you're probably dead :wink:
I've done loads of trackdays by myself, 'tis a good laugh and you meet loads of new people that way.