Diamond bolts are very expensive exp, around 300 coins loss per cast, for 67 xp, that 4.5gp for 1 xp, this is if you but unenchanted bolts and enchant them, if you make your own bolts however, you make a small profit (cutting you own bolt tips), if you buy the bolt tips, but still make your bolts, you lose money, but less then just buying your unenchanted bolts.