Going rate?

The case - You can buy non-limited slip complete chucks for $200. A cone type Sure Grip I'd buy if the price was cheap enough. In that one's condition, I'd pass on. The problem is not they "can't be rebuilt". They can. Once, usually, and they are never "as strong" as when true new. Basically they'll work for a while, and it tends be a shorter while. The problem is that as they wear, they produce only metal particles that in turn go through the bearings and gears themselves. So the whole thing is junk once it's slipping. If you want to build a "489" case, buy a non-limited slip unit, add all new internals, and go have fun.