You'd be better off going to Creeper to sell stuff honestly, he's got 5k seller gold and will buy items for exactly what they're worth iirc. Enchantments are listed from lowest to highest Enchanting Point cost. This is a disambiguation page-a navigational aid which lists other pages that might otherwise share the same title. However, with 110 enchantment skill you get 300 casts out of it.
However, for enchanting a weapon, you're always going to do more with a damage enchant than a constant effect enchant.