I'd be more worried about making poison so available to lower-level PCs in terms of combat rather than as a money-making machine.

I refer once again to 'Wood Shape'... A low-level pc can easily craft a masterwork mighty composite longbow with a strength bonus that would cost hundreds on the open market, more than some poisons... And it's something that can be used again and again... The spell is also my Druids own creation, and she is unlikely to teach it to any non-druids, if anyone at all... The pcs must also track down the focus for the poison as well, not so simple for low-level pcs...

If Wood Shape could make Masterwork weapons, any PC could approach a druid to have a masterwork quaterstaff created for 20gp then resell it for a 90gp profit. Repeat until rich or the druid or the DM realises something is up!

Indeed... The innovative use of a much overlooked spell...

Hmm...good points. My comment below didn't think about high-strength-rating composite bows. Needing to kill a wyvern before you can use the spell to make wyvern poison is definitely a balancing factor!

First of all, by nature a composite bow is not made from a single piece of wood, or even entirely out of wood in most cases. Wood shape couldn't do it for that reason alone.

Fromthe Wikipedia entry on composite bows:
"A composite bow is made from various materials laminated together, usually applied under tension."

From the SRD, emphasis mine:
"Wood shape enables you to form one existing piece of wood into any shape that suits your purpose. While it is possible to make crude coffers, doors, and so forth, fine detail isn’t possible. There is a 30% chance that any shape that includes moving parts simply doesn’t work."

I'd doubt that your bow will be terribly masterwork, or that your catapult will hit what you are aiming at with any degree of accuracy.

Your argument is sound, a composite bow, by nature is composed of different parts... I used Mighty Composite Longbows as a catch all... Not all bows with a strengh rating have to be made from different parts... You can make a bow with a strength rating from one sturdy piece of wood...
As for masterwork, yes, Fine Detail isn't possible, but how finely detailed does a quarterstaff have to be to qualify as masterwork...? You certainly don't have to have all sorts of engravings and decorations on it, it's just a long piece of wood that you pull out of a tree... As is a bow, though it would be slightly curved... At worst, I would have the 30% chance rule apply when trying to shape masterwork items, as well as a few ranks in Craft:Bowmaking... As for siege weapons, I may have exaggerated slightly, but I wouldn't rule it out... A high-level druid could certainly shape that much wood, and it doesn't say that you absolutely CANNOT have moving parts... Though maybe a few ranks in Profession:Carpenter would help... I thankyou for your constructive criticism...

Hrm, for the quarter staff, weight distribution is important at least. As a rule of thumb, I'd say you'd need Fabricate for that job.

I'd make it Transmutation rather than Conjuration: Creation. You're not magically creating a new substance, rather you're taking an existing material and transforming it into a new, more user-friendly shape.

I might also make it 3rd level on the basis that poisons are generally much more expensive than wooden weapons or shields - even MW ones.

Then again, if a Druid decides his whole purpose in the game is to turn into a poison merchant, maybe he's playing the wrong class ;)

Hmm, you're right... Transmutation it is... As for being a 3rd level spell, I'm not so sure... They DO have to track down a not-so-easy-to-come-by plant or creature, and know what it is in the first place. Plus, only one spell can be cast on any given focus... Because of it's casting time, it can't be employed mid-battle... I will think longer upon it...

To be fair, it IS kind of borderline. What kinds of spells will be competing for slots with this spell at 2nd or 3rd level? Or will it be one of those things where "Hey, guys, we just killed a wyvern...let's come back to the corpse tomorrow after I've prepared my poison extraction spell."?

You could add a time limit. Maybe the poison must be extracted no greater than 1 hour per druid level, or a flat limit of 1 hour.

My Druid likes to use poisons only derived from natural sources, ie plants, fungii, animals... Also, being immune to all poisons at 9th level, I love the idea of coating my hands in black lotus extract then wild shaping into a dire lion to smite the enemies of nature... She wont be selling any poison she makes...

I disagree with your thought on Wood Shape. The RAW (PHB page 303)specifically say that while the spell can make "crude coffers, doors, and so forth, fine detail isn't possible." A Masterwork item is described as "exceptionally well made" in the glossary. For my games, I would have to rule that creating a masterwork item would be impossible without fine detail. There is a tremendous difference of course between a masterwork bow and a "crude coffer".

Other than the change to Conjuration as you've already spoken about in this post, I would say that the poison would have a 'shelf life'. This would also limit it's misuse. A Craft check of some kind (probably Alchemy if nothing else, but Herbalism or Poisons come to mind as well) could mitigate how long the poison you make would be viable.

Of course, when you get right down to it, a Knowledge and Craft Poisons check could be used to simply find the dead creatures poison sac (for lack of a better term) and make it viable for your use. But spells are better!

Nice idea.