i have dealt with a company named northern auto parts and they have great prices on engine kits. i think for a stock 350 engine kit, it cost me around 150.00, for everything. pistons were cast, rings, cam lifters, gaskets, bearings, oil pump, timing chain. it was a good kit with brand names. you can't beat that for a stock rebuild. they also sell performance kits for starting around 300.00.
check them out at: www.northernautoparts.com
I'll second the recommendation on Northern Auto Parts. They have both stock and performance kits that come with quality components for great prices. Also, if you want to substitute a different cam or anything else into the kit, they will do that for you to.