Popular Mechanics had EMP weapons as their August 2001 cover story.
The article stated something to the effect that an EMP weapon of moderate yield could be built for about $400, including a GPS guidance system. Eliminate that, and the cost drops to somewhere around $100-$200. The rest of the device (both as mentioned in the article and shown in the cutaway diagram) consists of batteries, a capacitor bank, and a single, large (appprox. 3 ft long and 6 inches in diameter) copper flux compression generator. They are supposedly tuned to frequencies that somehow get through Faraday cages.
It is disturbing how easily anyone with $200, the basic electronics knowledge taught in any high school physics class, and soldering skills could build one of these.