Well it depends on what you want them for, I like to think of them in a few categories.
First you have your cheaper types that cause a disruption but don't kill your target right away. Price is for two coated arrows or bolts, not including the arrow itself for ease.
Paranoia - 3 Silvers - Disrupts the enemy lines, great for trying to get folks to stand-down or at least not work together
Weakness - 5 Silvers - More rare than I'd expect, but weakens most to the point where engaging is far safer. Tends to work on a lot of creatures that don't breathe gases in.
Next you have your take downs.
Laugh/Nausea - 6/7 Silvers - Will shut down most targets quickly, although the laughing tends to get to some people, I'd suggest Nausea, it's worth the extra silver although a bit more messy.
Vertigo - 8 Silvers - Same as above, but no mess, or annoying laughter, plus it's funny to see them fall down.
Feeblemind - 8 Silvers - More expensive, but will also generally shut down casters that can self heal from other ailments.
And then you have you simple Vorpals
Nice - 1 silver - Makes the arrow hit a bit harder, about what I'd do with a longsword, warning, I am not very strong.
Nicer - 3 Silver - Makes the arrow hit much harder, about a stone bolts amount of extra damage, although not as cool as a stone bolt of course.
Nicest - 4 Silver - Like the nicer one, but even more nicerest (I know it's a fancy word, trust me it's a craftsman term) Adds about a Lightning Bolt worth of damage, but again not as flashy.
Finally the Super special "Werehunter" Arrows, these are both silvered and have the best vorpal possible - 6 silvers per two.
I should be able to handle about 10 arrows of any of these, heck I could handle a full twenty I suppose.
Arrows are a copper a piece I guess I should say as well.
Regards,
-Kalith Toovir