Those prices are fine. Fancy mounts are usually pretty expensive in games.

Though as for vendor unlocks, I think they should have included more like exclusive vanity pieces, a few unique i70 gear pieces for gil (since darklight is common anyways) or maybe even materias/food.

From my experience with other MMO's, the daily quest vendors even unlocked a single BiS accessory piece or high end materia at max rank. This encourages more players to grind and generally keeps them subbed longer.