I got a mechanical keyboard for $0.99 shipped. it's razer so it's normally pretty overpriced at something like $80.
found 4 IBM Model M's in a dumpster (I was looking specifically for them - the guy that threw them out told me about it).
But otherwise, in non technology arena, I'd have to say for $15 a dive bag, but, without the store's understanding of what they had, a complete set of dive gear. Real world value was around $800.
In gaming, a vacuum cleaner box for $20. Same store as above, and inside was an original Nintendo Entertainment system (unboxed), and a slew of games, all complete in box, including Super Mario Brothers, SMB 3, Legend of Zelda, Legend of Zelda 2 (both Zelda games were the original Gold cartridge releases), SMB & Duck Hunt, Mario Golf, Excitebike, and several other games. It also had 4 standard controllers, an NES Satellite, 2 Nintendo Advantages, the original grey zapper (before they had to switch to orange for "safety" reasons), a dysfunctional R.O.B. toy (which I took apart, cleaned up, and then it worked - batteries had failed and a lot of whatever's inside had leaked out all over the toy).
Best deal I almost got. Brand new, never opened, Final Fantasy for the NES for $5. I *GOT* it for $5, but the SOB behind the counter OPENED IT, to make sure that everything was in the box. He thought it'd been resealed. I still have the seal - it's the original H seal on the back that CAN'T be faked or reproduced. Value now, in current condition around $60 - 80, value if it had never been opened $300+.
2 Famicom Edition Game Boy Micro's, brand new in box, for $15 each from a store that was going out of business. A lot of 7 Dreamcasts for $35 (still have 2) that ended up mostly working (5 good ones, 1 functional but the lid was messed up, and one that wouldn't power on). a mega crap ton of Dreamcast accessories and games, (though I've lost my favorite of the bunch, which was Seaman with the microphone - I have no idea where it disappeared to) in a lot for $100 (20+ games and numerous accessories, all original Sega branded, including 4 standard VMU's, 4 colored VMUs, 2 grey controllers, 1 blue 1 red controller, 1 rumble pack, keyboard, mouse, sega bass fishing controller - works in almost all games, it's hillarious). The only peripherals I'm missing for my collection now (that I don't have at least 1 of) are the Seaman microphone, and the broadband adapter.
Also snagged a $1000~ HTPC by ASrock for $225 from a pawn shop. Bought a Monster's Inc. Sullivan dressed as Santa Claus for $3.75 and sold it for $75 later that month. Bought 2 Balto plush (the small and the large) for $2 each, and sold the large one for $80 (needed the money sadly), which was valued at $125 at the time. The small one is still worth about $80-90.
I bought the world's first HD-DVD / Blu-Ray player (at the time MSRP was $1500 I think - might have been closer to $1000), for $75 at a salvage center. The box was water damaged, but the product was fine.
I do a LOT of this kind of shopping, so the list goes on. For those that think that I'm very lucky - it's kind of lucky, but considering the sheer amount of time I've spent shopping with NO success, it kind of evens out a bit. I'm still amazed at the diving gear and the NES lot - same store, same day. Later that month, I found an diving scooter missing it's cowl (it works, just needs the outer plastic to make it waterproof), and was about $3000, that I got for $15 ish from that store. Unfortunately, company went out of business, so I keep looking for broken models just to get the cowl on it.