I must have been lucky over the years. The first deal I got (which sounds like a deal now, but at the time was pretty common) was an Enfield .308 model bolt rifle with the detachable 10 round magazine. I think I paid somewhere around $100 for it. After some research, it looked to be manufactured in India in the early 1970's. I sold it for 3 times that when going through a divorce and I've tried buying it back for years, but the friend I sold it to won't budge.
I also got a SR1911 commander shortly after they came out, in .45 ACP, used but in LN condition for $375 from my favorite LGS. They were going for around $550 new at the time I think. It didn't even appear that it had ever been shot.
Then, I once found a Rossi M92 in .357, stainless, used at another LGS for $375. I think they were north of $500 bucks at the time, but I could be wrong. Either way, it was a deal. I liked it ok, but then got an even better deal when I traded it for a minty S&W 686-something, snubbie, complete with 3 speed loaders and a nice leather OWB holster. I felt like I came out great on that deal (flat trade). However, at the time I was looking for a semi auto carry gun and traded even with a LGS for the brand new (at the time) XDs .45 (which I have since sold and replaced with a SAA clone). I still regret trading the smith.
Lastly, my mom and step dad's house was broken into a few years back and his guns were in a glass display case and rifle rack in the living room. For some reason, the thieves only took a couple black powder kit revolvers, I guess thinking there were cartridge revolvers, and left the shotguns and others behind. My step dad was sure they'd come back and the shotguns were left to him by his deceased brother so he didn't want to lose them. He sold me 2 shotguns and a very nice modified Ruger 10/22 for $250 bucks with the stipulation that I would not trade them or sell them. The shotguns are both Sears and Roebuck M200's, one plain with the 28" barrel and one Ted Williams model with the poly choke, vent rib and double site beads. The shotguns are like new and look like they were just pulled off the shelf. By far the most smooth pump actions I've ever felt. The 10/22 was modified with an aftermarket stock and decent scope mounted. I feel like that was a deal.