That sort of neglected lathe can be a great bargain. Since it hasn't been used in that condition, as long as you disassemble it and put the bits through an electrolysis bath, the rust is normally of little consequence, and the bed will not have any wear from this last "owner". Bummer if it was already a clapped out lathe before it got to that owner, but the risk of buying it is low.
In the UK you have a lowest prices for wonderful old lathes. Here in Austria, nothing much goes for under a €1000. I consider myself lucky to have picked up my Boley 4L for €950, although the change wheels are missing, and the bed has some wear and a some nasty dings. Compared to the Chinese 7X I had before it is a dream to turn with.