I've been soaking up tons of info on zappers here, and thank you all for contributing so much experience.
I decided to order a $10 zapper rather than take the hours to round up the parts and build it, but couldn't wait to start zapping myself, so I generated a 2500 Hz squarewave with 50% DC offset (entire waveform above zero) on my PC using Cool Edit, ran the soundcard into an amplifier and wrapped a speaker wire around my toes. It helped to have a voltmeter which measures AC voltage so I could be sure I wasn't turning the amplifier up too far.
Just thought I'd pass that along since I hadn't read of any similar approaches. I'm guessing I can count on a certain interested party to suggest why this is all wrong and that perhaps looking into his commercially-available zapper might be a better idea. :-)