A 384:
Crafting poisons works the same as other alchemical items. It costs 1/3 the price of the final poison in raw ingredients, and you need to make a Craft(alchemy) check with the DC equal to the save of the poison you're trying to make.

Note while this works for every poison by RAW, it you may draw some raised eyebrows if you somehow create Dragon Bile out of the salts, acids and bases in your alchemy kit. Use common sense.