Turn one of your characters into a ninja (or, if you have a ninja, give the Throw ability to one of your guys), and then throw Bolt Scrolls like there's no tomorrow. The scrolls do 2000 damage or so, if I remember right. Just make sure you have a good White Magic user and you're all set.

You can buy Bolt Scrolls from Bartz's village. They're a wee bit expensive, but you should have money from all the levelling you're (hopefully) doing.