Obviously check for spark to help your peace of mind before making an offer. If it actually pops or fires up, see what they want for it. Sounds to me like a $200 saw if it's all there with no cracks/breaks anywhere and doesn't leak fuel and oil all over the place. If it doesn't even make an effort to run, explain how expensive it can be to rebuild, but you'd really like to get it running again...., (going for their sympathy and benevolent good will during this season of giving). LOL
Rule of thumb for me is offer what the bar and chain are worth if it doesn't run because everything else will cost you extra to make it worth much more unless you were to simply part it out.
All that said, you're gonna have fun with that saw!