You might stop by Clint's store (Brew Bros Hops and Sprockets) and see if he knows of anyone selling a used bike. Trek has some spring sales right now if you want to go new. I think Pathfinder has mostly switched to Trek. They occasionally have used and last season's bikes down stairs. A decent hardtaill will do fine on the river trails. You could probably do the trails at Fancy Creek depending on how aggressively you ride.
Used bike sites like Craig's list or Pink bike aren't real great in the area until you get to KC area. Jerry's in Topeka is okay, doesn't have a great selection, but they work to help you out. Capps is the worst of roadie culture. Judging by the people who go there, they pretty much suck. Been there and handful of times and found it unremarkable.
