To this day, I still remember finishing Mass Effect 2 and looking at the menu thinking, "Man, I wish I paid more for that game."
I'd picked it up during a Steam sale, back when flash sales were still a thing and AAA games were available for ridiculously cheap prices. You can still get good deals today, but the excitement isn't quite there. Publishers and developers are a little more savvy about tanking the price, these days.
But I loved ME2, much in the same way Uncharted 2 was totally my deal. The pacing was exactly what I wanted, and there was plenty of variety amongst the characters, missions and dialogue to keep me going throughout. I only paid $10, and I paid full price for Mass Effect 3 when it came out partially because I still felt bad I didn't pay more for ME2.
Another cracker of a bargain I remember was going to a bazaar in Sydney's inner suburbs - Lidcombe, possibly - where I ended up coming across CDs of FX Fighter and Savage Warriors. Neither game is particularly special - Savage Warriors is pretty terrible in a lot of aspects - but it was $5 for the pair of them, which wasn't bad given I spent several weekends learning all the combos.
What's the best gaming bargain you've ever picked up? What was it, and how much did you pay?