Most Oneworld and SkyTeam carriers have round-trip flights to various destinations in Europe at a discount today for $473-$558, with a connection. Dates vary, use the linked calendar. Cheapest fares are mostly midweek. Most fares are not reversible.
Notes: Fares are between November and April, but the exact ranges for each destination will vary. Use the Google calendar view to get an idea of what dates work.
Flights to smaller airports (Inverness and Milan) may require a long connection or two stops. When you begin your search, modify your filter to remove fares that have more than one connection, some of those smaller airports ONLY have flights with bad routing.
There is a good chance that other airlines will eventually match these fares if the sale goes on long enough.
