I built my own zapper for around $30 USD and have had some most positive results from its use. I downloaded the schematic and instructions from a link at zapperguy.com
Initally I started passing what appeared to be rice grains but know that they were parasites. I zapped everyday for several weeks until the (rice grains) stopped and now zap about once a week.
I bought a small plastic case with breadboard from Radio Shack and used that instead of the box and also used a copper water line cut to length for the hand grips; but it works just as well as I was faithful to the schematic.
You can order a zapper on the zapperguy.com web site for around $80 USD.