Good points TomOBedlam.
I was talking to my wife, a medical professional no less, and she says Drugs. There are common enough drugs that cause sleep, paralysis or even a flash bomb. At that point I am thinking "Why didn't I think of that!"
I have yet to see what is out there, but ever community has a herbalist. Usually large communities and small ones will have a herbalist on the payroll somewhere. Take that alchemist, also on the payroll and you can make flash bombs with the herbal concoction. All you have to do is train the soldiers (not all or maybe all if you are a small enough community) and you have a small army with a rather inexpensive payload devise and chemical weapons.
Choking powders, strong sleep agents, pepper spray sort of attack, etc.
I think a lot of us think in Terms of One offs. We hire an Alchemist, pay him to do a huge work order and suffer the drain on our accounts. Well I don't always think that cities would pay the powerful alchemist when they can hire a younger one looking to make a name for himself. On top of that cities do the same damn thing that my boss does "Hey Elrik, I have a friend that needs a network setup. Tomorrow, just head over there." I don't make extra money (grrrrrr) and my boss gets a happy buddy. Same for the herbalist.
In short, you get a decent alchemist and herbalist, put them on the payroll and give them things to do. I have done in several games as it was easier to get someone on my work sheet then to have to bring in someone special every time I needed something small done.
Even if you buy an expensive herb, you can mix the chemicals or even package them in such a way that once it is thrown, you get several smaller reactions. Maximize the effect by putting smaller doses of chemicals in the flash bombs.
I also don't think it should be super expensive. For the herbalist, you give her/him some land and tell them to plant what they can. Use what you have on hand to the best of your ability and move on. If you need to buy some super expensive herbs then do them in small quantities.
I think it is pretty easy to train a guard to throw a bomb in the right direction. "Just get it near them."
If need be, boil down some vinegar, put it in a glass jar and throw. If you have it, add some local hot spice to the mix. No matter what level you are, that has to burn the eyes.
That leads to other issues. What sort of RR does a PC get VS. a bomb attack like that. Unless you are superman it will burn and probably give guards a few moments to deal with you without interruptions. In the past I have denied PC's saves because I thought it was ridiculous.
Thanks for being involved guys!