Finnair and Iberia have round-trip flights from Chicago (ORD) to Prague (PRG) for $433-$457 with a connection. Flights March, April, May, and September. Departures on Monday, Tuesday, and Thursday. 7-day minimum stay required.
Some small OTAs on Skyscanner and Google have this for cheaper than the airline. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.