Guns compete with bows for the same hunter slot, and because many are engineering-crafted, gun prices track the ore market underneath them.
Gun (Weapon)
Auction-house prices and price history for Gun in MoP Classic.
121 items in Weapons › Gun are currently auctionable in Mists of Pandaria Classic.
Prices refresh daily from TradeSkillMaster (TSM), so day-to-day gaps in lower-volume listings are expected rather than a collection problem.
Gun listings link to price-history pages with per-realm buyout, average, and median data for Mists of Pandaria Classic.