DOD make some of the cheapest DI boxes ($30-$150). Basically, you are simply dealing with a transformer that converts high impedance instrument signals (unbalanced) to low impedance (balanced XLR) so that you can send it several hundred feet to a mixing board and still be able to plug another cord into an onstage amp. The main thing you need is a "ground lift" switch so that you can eliminate those 60Hz hums caused by the stage 110v circuit and amplifiers being on a different 110v circuit from the mixing console. If you don't need the feed to the onstage amplifier, you can get a high/low matching transformer (High 1/4" to low XLR) for $10-$15 from Radio Shack.