Icelandair has round-trip flights from Chicago (ORD) to Helsinki or Zurich (HEL/ZRH) for $435-$487 with a connection. Flights October to April. Extended weekends available.
Note: Some small OTAs on Skyscanner have this for about -$25 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.