big_pond,
It is definitely possible to build your own shocking system that works as well as the Smith Root. I know because I've used Smith Root units extensively and I've built four "homemade" units. I've also had quite a bit of experience with the old Coffelt units and other garage-built systems.
The heart of the system is a bridge rectifier, which can be had for about $15. The Smith Root uses exactly the same rectifier, embedded in potting compound on a heat sink, but they charge $350.
However, please don't ask for the schematics, I won't give them out because of liability concerns.
One other disclaimer, there's more to fisheries management than just having an operational shock unit.
