Hit percentage is all based on stats.
As far as power, guns > bows > xbow, and generally that order applies to price as well in terms of ammo costs. In terms of weapon costs, I'd say guns/xbow are about equal, and bows are the most expensive (+1 bows).
BUT, guns will ONLY do more damage when you get to Silver Bullets (lvl 55), before that, they aren't that great.
Best place to buy ammo is NPCs, which is almost always cheaper than AH. Bullets you cannot buy at NPCs (as far as I know) and go for 7k-9k/stack (lvl 1 Bronze Bullets).
So generally what most do is buy a bow and xbow, and level them both equally. Use your bow for primary damage, but keep the xbow on you for when you gain a level so you can re-cap it. That way if you want to use guns later on (guns/xbow = marksmanship) you'll already be maxed in that combat skill.
Edited, Fri Feb 20 13:00:14 2004 by defunkt