Made 2 separate trips to the CompUSA $4.88 sale and got 16 games each time.
But the single most games I have bought at one time was years ago when I stumbled upon a Computer City going out of business sale. This had to be like 6 or 7 years ago. I walked in with a friend and saw they were going out of business. Most of the big stuff was only marginally marked down, but the videogames were 75%-90% off. I ended up getting about 25 Sega Saturn games and a few for other systems for about $100. I would have gotten much more but a scalper had already hit the other systems, including Playstation which I didn't even have yet at the time, but certainly would have bought some because I knew I was getting it. He was just throwing every copy of every game in a cart that I had thought was just excess stock until I started looking at it and he nastily proclaimed it was his.