I've used the Mission Community Center as a guest a couple of times. Not bad, but not sure how much it costs or if you can even join without living there. It's not 24 hour. Free weights, machines, track, four basketball/volleyball courts, two racquetball courts, big ol' pool.
I think there's a 24 Hour Fitness at 75th and Metcalf. My gf's bro used it one summer and seemed to like it okay.
Overland Park just opened up a new community center in downtown:
http://www.opkansas.org/_Res/Parks_and_Recreation/Places/Community_Centers/Matt_Ross/index.cfm. Looks like you can join for $88 for 3 months ($29/month), $27/month paid monthly (year-long commitment), or $295 paid in full for a year (~$24/month). But again, not 24 hours.
Edit: I misread and thought you were looking for a place open 24 hours. Upon rereading, I think you were just listing the price for the 24 Hour Fitness. My bad.
