I have great luck buying boxes of fasteners removed from GM 60's 70's era vehicles.... Usually find boxes for $5-$20 at flea markets, quite a few times there are RC15 rad caps and Stant Assembly line Gas Caps thrown in, last box I bought for $10 had 2 original Cowl induction relays along with really nice rear spring shackles with bolts and the original mardsen nuts.
You be one lucky guy as I go to both small and major flea markets (Carlisle and Hershey being large) and never see boxes of fasteners being sold as you mention. I need to go where U go! LOL But do agree that when I have found some good stuff cheap its been in the $1 or $2 bins like correct battery hold downs, etc..
I bought a 9 M10 437 Ls6 distributor for $10 at Charlotte this spring on Thursday morning, then 2 NOS RS actuators and the remainder of original RS components hoses T's - RS HL washer parts, RS plastic shields and brackets for $100.