A MK3 would be great, but might prove a bit more pricey than what you're after. If you're thinking about changing the engine anyway, I would look for a MK4 or MK5 - These are mid 80s cars. These seem to be the cheapest to buy at the moment.
Either way, I would spend a bit more on a decent shell. If you don't spend initially, you'll end up spending in the long run on more panels etc!
Also - M-Machine are brilliant for panels.
