American Airlines has round-trip flights from Houston (IAH) to Chicago (ORD) for $97, NONSTOP. August to December. Origin/Destination reversible.
Note: Carry-on bag is allowed for free on American Airlines. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.
Note: Spirit may be matching with fee encumbered fares. Avoid those unless you have a way to get around carry-on bag fees, seat selection fees, and various other fees.