Any of the classic valve games (half life, portal, and their sequels). If auto shooters are your thing, vampire survivors is less than a small coffee. Dead space (the remake) is $15. Halo MCC is $10. Titanfall 2 is $3. The “new” tomb raider trilogy are all less than $5 each or get the bundle. Alan wake is $5. Prey is $3. And Batman Arkham origins is $2.

Just a handful of good games for cheap. There’s many more out there.