Like Cat It is hard to load for less than you can buy common stuff unless you get really into it, powder in 8# kegs, wads by the case and shot by the ton.
The best prices are either at a local trap club or if there is a lot of trap shooting in your area there is usually someone that specializes in case lot shot shells and components. I have a place called Connies Components out here plus you save on hazmat shipping charges.
I also buy from:
Ballistic Products, ITX shot (soft non-toxic for my old guns), wads for 2.5" 12 & 16ga, 2.5" 12ga hulls and Nickel plated shot.
Precision Reloading, Bismuth & Nice shot (again soft non-toxic for older guns)
Graf & Son 16ga hulls 2.75 and 2.5 inch hulls, they have great shipping rates and oddball stuff. I get my 7x57mm Rimmed and my 9.3x72mm Rimmed ammo there.
I load only for the odd stuff, low pressure 12ga & 16ga for old SXS's both 2.75 and 2.5 inch in lead and non-toxic for lead free areas. I buy all my trap and skeet loads by the case, B&P even has 2.5" light loads and they ship free to your door. Cabelas has a new Herter's line that has 16ga shells at a great price and I order by the case and pick up at the store to save shipping.
The Lyman book is good and Ballistic products has a book called "Advantages" and it has an incredible amount of load info, even has 2" 2.5" and 2 5/8" roll crimp data for European and British guns plus they have pamphlets on roll crimping, fiber wad loads and coyote/self-defence buckshot.