I agree with Deejay that the one you have been offered is a project rather than a mower, and the asking price is in my opinion quite excessive. If the chains and sprockets were good, I think it would be a decent proposition for an enthusiast at $100. If it needs sprockets, I would value it at zero, since at least in the eastern states you can probably get a decent SB mower with a Briggs engine and a catcher for about $150 if you spend some time, though probably only a 17".
My uncle used to have an extremely rare antique ex-factory-team racing car, which unfortunately he had modified rather severely when he first bought it in the early 1950s. In later life he wasn't all that attached to it, and a friend wanted to buy it from him, but the friend was able to prove that it would cost more to fix it than it would then be worth. Uncle saw no purpose in giving it away to someone who would then brag extensively about having got it for nothing and brought it back from the dead. The eventual solution was that my uncle died and my brother and I reversed all the damage he'd done then auctioned it unrestored for not very much. If you'd costed our time spent fixing it, it probably barely broke even as a repair project. Messed up collectors' pieces are a lousy investment compared with one that is just decrepit but does not suffer from "tenant's improvements".
