i bought a saxo mot failure for £200 spent £100 on it to get it mot'd and just sold it for £500. it can be easyish money if you can find those sort of cars.
i also a few years ago built a saph cosworth rep it stood me at £1000 done and swapped it for a focus estate which i sold for £2000
im just on the look out for my next one but they seem to be getting hard to find