I had upwards of 600k...
Didn't want to spend any but a spectral tiger appeared in the ah and I've loved the mount since bc. Then a goblin rocket and onyx panther later I was at 100k. I don't regret those purchases. Especially now that tcg is canceled. The only other big purchase mount I would like is myrmidon's head. I don't think hearthstone will be bringing any high priced mounts to the game. So maybe think of a mount you've always wanted or a black market item.