The easiest way to catch the shad is with a gill net.
Many of the catfishermen order the gill net from
The Fish Net company
Stock number is: LGM-6617 Price for 6' x 50' is $46.91 less shipping.
Mono 6' X 50' long.... 2" Mesh 3 1/2" Stretch.... 3/8" Float Rope.... Leaded Core Bottom Rope
Call Billy @ 800-256-5256.
I would think you would be better off with sticking with a 50ft net. If you go out a lot by yourself a 100' net would be hard to pull in your self.
Also you have to order your floats separate. I forgot the stock # for my floats, just ask Billy what he recommends. Virginia regulations require that you use at least a 3.5 diameter float on each end and painted a florescent/reflective orange. I ordered ....(2) 3.5 and (2) 4" floats just to see which I like better and ended up putting all 4 floats on my net.
The last 4 numbers of his/her social security number or driver's license number (at least 1"high), preceded by the letter "R"
More info:
http://www.jamesrivercats.com/gill.htm
Jerry
Maybe I'm missing something but the Gill Nets don't look cheaper than casting nets on that page?