Well, the stock Noble in the MM has 2d8 HD, with 9 HP, and a Con of 11. But the Knight's got 8d8+16 HD, with 52 HP and a Con of 14. Archmage has 18d8+18 HD, with 99 HP, and a Con of 12. There's your scale of regular folks you might want to poison.
Now, the three top end poisons are Midnight Tears (DC 17, 9d6 at midnight, ingested, 1500 gp), Purple Worm (DC 19, 12d6, injury, 2000 gp), and Wyvern (DC 15, 7d6, injury, 1200 gp). You might want to add Pale Tincture (DC 16, 1d6 every 24 hours, no healing until you make 7 successful saves, ingested, 250 gp), just based on effectiveness. The rest of your mid-range DCs and prices are mostly Poisoned and Unconscious/Blind/Paralyzed or something, which, you know, nice in the right spot, but very much "conditional effects for a fight" rather than "fight enders".
Looking at the range of injury poisons, you've got two low end ones: one that does 3d6/DC 11, and one that does Poisoned & Unconscious if you roll low/DC 13, and the two big ones (Wyvern and Purple Worm). For ingested poisons, you've got your high end (Midnight Tears and Pale Tincture) and your low end (Assassin's Blood-1d12/DC 10/150 gp), and a couple of effect-based ones (one "truth serum", one "poisoned for a few hours"). You've got a couple of contact poisons (both just effect-based, poisoned and paralyzed or unconscious, DC 13), and a few inhaled poisons (two effect based - one knockout, one blinded, and then one damage based 3d6 and then 1d6 per turn until save, DC 13).
So, I dunno. I might tweak the pricing a bit, but I might just leave it alone. The crew I'm running right now aren't really the poisoning types, so it's not a major issue.
As far as the world at large, Pale Tincture is really the winner for your basic assassin for hire, trying to take out somebody important. The rest of them, I can see as occasional trap components, but they're really kinda expensive for fight add-ons. I suppose that might be the point, though, pricing them out of the game for most party foes.
