Around 40 games for gamecube I believe, most bought at full price. Generally, I bought a game every 1.5 months.
My previous system with the most amount of games was dreamcast with around 30, but many bought on sale or used, plus most dreamcast games were only $40 anyhow.
Then n64 at around 20, most new. Well, I think I had a lot of used NES games (most bought for under $10 cart only) but I don't remember how many.
However, the difference was my n64 and dreamcast buying also included a lot of PC buying, but my PC game buying has greatly downgraded over the years, and was at its peak during the n64 years. Though as my disposable income has increased, I suppose my game time had increased as well, though my free time has decreased significantly. Don't really buy many games anymore, not nearly as quick as I used to. I don't really need to find things to occupy my time now, so I tend to only buy games that are quick and really fun for the short amount of time they last.