This seems to be a fair price if the rust isn't too bad. Bonus points for it being a manual and having the NP205.
https://denver.craigslist.org/cto/d/denver-1978-gmc-jimmy-full-size-k5/7276225252.html
https://denver.craigslist.org/cto/d/denver-1978-gmc-jimmy-full-size-k5/7276225252.html