I found these pages extremely helpful when deciding on if an item in the AH was a good deal or if i should just buy a piace of equipment and upgrade it myself.
http://rappelz.wikia.com/wiki/Weapon_Costs
http://rappelz.wikia.com/wiki/Armor_Costs
http://rappelz.wikia.com/wiki/Shield/Helmet_Costs
http://rappelz.wikia.com/wiki/Glove/Boot_Costs
http://rappelz.wikia.com/wiki/Belt_Costs