Part of the reason the Goldeneye is so expensive is that the Grazelanders don’t part with them easily. They are sacred to the Pure Horse People. That being said, I suspect that these ARE the horses of the Grazelanders. They are also the basis of many of the horses for the Pol-Joni. I doubt the Grazelanders sell non-geldings to outsiders. Any breeding stock needed to be stolen.
From the Smoking Ruins and other stories (2019), Encounter with Grazers by Dimitrina Angelska
Given that Grazelanders eat horses rather than cattle, would a Grazer really eat a sacred Goldeneye? I suspect Goldeneye horses are eaten in the following two manners:
Religious rituals. Sacred horse sacrificed to Yelm or Hippoi and eaten by the tribe in a group ceremony.
Regular food. Mainly lame or elderly horses. Again sacrificed to Yelm or Hippoi but then distributed among the tribe to be boiled in a stew.