I've never paid more than $50 for a core, and these days I won't even buy one, I build them from new parts including an SFI case. For drag racing, a 1.82 stock gearset is pretty much junk. Anybody making any real power will kill it very quickly. The 1.76 gear sets hold up decently under moderate hp levels and lighter cars, but when you really start making power, aftermarket sets are the only smart way to go. I've seen the 1.76's survive in 800 hp applications, but they don't last long......another issue is the case itself....they are decades old and have been known to crack or break....
That being said, a stock case glide with the 1.76 gearset, PROPERLY assembled with some upgrades can last a long while in many applications. A version with a 1.82 gearset can as well as long as the power is limited and the trans isn't abused.
If it's your intent to keep it, get the book from Carl Monroe on power glides, it's money well spent. If you're going to sell it, take it to a local or nearby track, ask $200 or best offer, and you'll likely walk away with and easy $50-150 in your pocket pretty quickly.