I second the train option. If booked in advance consider it even for Paris to Switzerland. Direct TGV's which for sure will be cheaper and probably faster too than a plane considering checkin and going to the airport. Check www.seat61.com for all you need to know about trains.

The other suggestion which might actually be the cheapest of all is to rent a big SUV or van that seats six. Just make sure they are equiped with the required things for all countries (tyre chains!). The highways are good quality, and if you are OK driving in snowy areas it might be the best option.