Graveyard bowling: $2 shoe rentals and $1 games. Unless you're a senior citizen or part of a league this is an unbeatable price.
I try to make this part of my Vegas trip every time I go. It's a cheap, fun activity that does very little damage to my wallet and kills a good amount of time.
There are a ton of lanes, and the bowling alley is clean and well maintained. Even though there are lines at times I've never seen anyone relegated to a waiting list.