How much is a 4 speed core worth?

Are any of the gears broken in it? That's about the only thing that would give it a rock-bottom "core" price. If it is a B-body 4-spd as you say, get on
forBbodiesonly.com for a buyer. They don't easily fit A-body cars. Even the standard 23-spline 833 is a very tough buzzard! I have seen them at swap meets for $300 with the side cover off for inspection. The 18-spline version is much sought after because this is the so-called "hemi 4-spd" that was available in two versions: white stripe and red stripe. I haven't seen any of these lately for under $700. If it is indeed a "core" you have, it is only worth whatever someone is will to pay you for it.