You're in Vegas so yeah, you are going to spend (ie. lose) money. So why not go old school and spend some quarters but have fun doing it! It's kind of a dumpy joint but who cares! No cost to get in and it's jammed packed in there with pinball machines. There's also a few claw machines and video games too.
The machines date from the 50's on up and cost you from one quarter up to two dollars to have as much fun as your skill will allow you. It was fantastic seeing machines with the old fashioned clink clink clink counters along with modern machines with all of the goodness Bally could shove into a machine. Each machine also has a sign on it giving all of the details about it which was very interesting.
I came in humming Elton John's pinball wizard and after putting a fiver into the change machine to get my quarters I went nuts! Oh yeah, I was putting body language into those flippers :) Depending on how good you are at the games you can get away with having fun for a long time for far less than what you'd put in a slot machine.
Get off the strip and take your money here to have some good old fashioned fun.