The first place that comes to mind is Loco Joes. There's two locations within about 10 minutes of downtown Des Moines and one within 20 minutes in Ankeny. You pay $2-3 to get in and then every game costs 0-6 nickels to play.
All of the malls and truck stops have a game room and so does most hotels. Many bars will have a pinball machine also, but those tend to be a bit pricey. A
partial list of places to find entertainment is found
here.