Leather serves rogues, druids, monks, and demon hunters, and leveling leather often outprices equivalent mail because more alts want it.
Leather (Armor)
Auction-house prices and price history for Leather in MoP Classic.
1,818 items in Armor › Leather 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.
Leather listings link to price-history pages with per-realm buyout, average, and median data for Mists of Pandaria Classic.