I got my running and driving blazer for $3800 4-5 years ago. Now after all I've done to it, which is a lot, I have it listed for $14,500. Honestly it's probably a 10-12k truck but I don't care, partly because I don't really want to sell it all. But if someone comes my way offering me $14.5 I may just take it.
And browsing local adds the asking prices are really all over the place, especially for Blazers 76-87, first Gens are always expensive and the 73-75 as well. That does make it hard to price your vehicle. But I'm sure as hell not giving it away for $6k either.