Granted none of these finds are on the level of finding a copy of stadium events sealed for $10 or getting 5 sealed copies of bubble bath babes for $25 apiece, I've gotten some pretty sweet deals in the past 6 months. Here's just a few of them.
.Hack Quarantine, .Hack Mutation, .Hack Redemption, .Hack Outbreak, Shadowhearts from the New World, Shadowhearts Covenant all cib for under $100 (Quarantine alone sells for $80 minimum complete on ebay, has reached as high as $120; others are worth between $25 and $50)
Jurassic Park Operation Genesis (xbox), Jojo's Bizarre Adventure (ps1), and Fire Emblem: Path of Radiance (GCN) all complete for $20. (Op Genesis sells for between $75-120 on ebay, has been going up since then; Jojo sells for $30; Fire Emblem sells for between $50-75)
Mega Man X2 w/manual for $30 (sells for $100+)
Dragonball Z Budokai Tenkaichi 3 complete for $8 (sells for $40)
Those are just a few of the good deals I've made. I dug around my basement and also found some pretty hardcore collector stuff. I found the box and manual to Mega Man 6, Pokemon Red Version, Pokemon Yellow Version, Mario Party, Goldeneye, Castlevania 64, Legend of Zelda Ocarina of Time Collector's Edition, Legend of Zelda Majora's Mask Collector's Edition, and several other games. I also found manuals to Super Mario RPG, Mario Party 2, Quest 64, and several other games.
I have a rule in buying games. If I want it for my personal enjoyment, I'll pay whatever price it takes to get that game. If it is strictly for my collection, then I enforce a $15, $20, or 30% rule. If the game is worth under $20, I'll buy it for half the true value, or walk. If the game is worth between $20-40, I will buy it for $15 or more under true value, or walk away. If the game is worth between $40-75, I'll buy it if the price is $20 or more under true value, or walk away. If the game is worth over $75, I'll buy it if the price is listed at least 30% less than true value (could be more or less depending on the rarity, could also be 20% for a game like Stadium Events), or walk away. With that system, I will never lose money. And if I can buy a game and know that I can flip it for a quick profit easily, then it will be bought, no matter the cost.