| Painedbood |
I am against using the survival skill to extract the poison, but it does make sense to a degree.
Take gutting a fish. Normally you do this before cooking, and all the nasty insides come out. This is not surgical precision, but it is gathering food for survival.
You could argue that skinning and animal requires surgical precision, but it doesn't. The fatty tissues make this really easy, but preserving it requires a good deal of expertise.
I would argue that if you are going to use Survival to allow for the extraction, you could logically require a knowledge check to verify if you understand the anatomy of the creature or plant well enough to pull this off. The same could be said for the Heal skill.
Otherwise, high DCs are a decent way to increase the difficulty and represent how hard the task is.
Now for the important part. I have worked in medicine. Without a lab and specialized tools, you are not extracting any "sack". There is a reason animal handlers milk the snakes, even the dead ones. It is near impossible to do this type of surgery reliably. This is why puffer fish is so expensive and takes all day to prepare. And even then, they actually remove a proportionally large amount of meat to ensure they do not rupture the gland.
Even if you succeed, you then have to be able to transport and dissect the sack in such a way as to not spill the poison everywhere. I have literally seen a child milk a snake. Unless there is damage to the gland or delivery system, it is easy as long as you have thick leather gloves and specialized milking bottles.(The only real specialization is a type of cap that keeps it from splashing back out at you. Poison actually ejects with a decent amount of force.) It always annoys me when characters in RPGs go around collecting poison sacks from the creatures they kill. It doesn't happen.
Point of fact, "Animal handling" makes the most sense for extraction.
Key things to remember are expertise, time, tools, and cost.
There are many different types of creatures and plants that are poisonous, and just because you know how to milk a snake, doesn't mean you know how to milk a spider. Even if you do know, this does not mean you will have the physical ability to do so.
It takes time to extract the poisons and they do break down rather quickly if not preserved. Most bodily fluids do.
There is a reason most jobs have a specialized tool set. You might be able to make do, but some tasks are impossible without the proper tools.
Assuming you have the expertise, time, and tools, the remaining cost comes from the preservation chemicals. The book gives a generic cost various poisons (as well as the rules for crafting), but this assumes you are starting from nothing. If you already found the most crucial piece, some or all of the cost should be negated. For many creatures, you can and should take this out of how much they are worth.