Not in OKC per say, but Guthrie has probaly the cheapest rentals in the area. Crabtree Aircraft is who you need to look for. The airplanes are definitely older but they take good care of them.
When I was there a 172 was right around $100. Oklahoma Aviation at PWA was asking in the high 100s for their glass 172, and Air One was somewhere in between.
Oh, by the way, Guthrie is only about a 25 minute drive north of OKC just in case you aren't from the area.