Agreed. I was going to make poison use regular with my level 12 rogue, but even with the large amounts of money we get from loot, spending ~700 for a single dose of a good poison (ie, high DC) just isn't worth it, considering I can get a magic item that gives me an ability x/day that is just as deadly.
Even on limited use items your money might be better spent on, say, a necklace of fireball. There are even animal-summoning tomes that, yes, can be costly (16k for the best kind), but can do a lot more damage for you and are not single use (10x/week usage).