Your best bet, if you want a quick turnaround, is to find a local Lego AFOL group near you. Pretty much every major US city has them, and Europe as well, I think. Best not to be too obnoxious on the discussion board itself, it’s generally best to mention which set, and then invite interested parties to contact you off-list.
Second quickest is craigslist, usual caveats apply. I’ve also seen sets at pawn shops, if you’re OK going that route.
Bricklink.com has some pretty good tools to see how much money it might be worth (depending on how complete and what condition)
Good luck!
