Not sure if it's really economical or not, but i leveled BS from 280 to 300 using thorium helms. I then sent the helms to my enchanter to disenchant (the occasional nether essence paid off nicely). to craft a thorium helm it takes 24 thorium bar, 1 star ruby, and 4 yellow power crystals. It wasn't too awful finance wise. But there may be a bettter way.