Your best bet for afforadable apartments is going to be Maryland Heights/Creve Coeur or North County/Florisant(just make sure you go far enough north) area. Either one has a 15 minute drive to the airport. While St Charles is nice, its a longer drive and I believe the apartments tend to be newer and more expensive. Lots of my coworkers have bought homes and condos in the new developments out there.

I concur on Chesterfield being expensive. Tends to be full of doctors and such. Even the south western corner of Creve Coeur gets pricey. In Maryland Heights, stay away from West Pointe apartments. They are cheap, but the management is not tenent friendly. Pheasant Run off of Dorsett is low priced and backs right up to Creve Coeur lake.