The cheapest way in. The Welcome Pickups transfer to Interlaken is 17 minutes quicker for CHF 219 more, which is not worth it at this party size.
IC81 to Interlaken Ost
IC81 · SBB, on a point-to-point ticketPickup, hours & luggage
Boards at. Zürich Flughafen railway station, platforms 1 to 4 — the InterCity showing Interlaken Ost
SBB's point-to-point fare, not a ZVV ticket: CHF 77.00 an adult in 2nd class (CHF 131.00 in 1st). Children 6 to 15 and Half-Fare holders pay exactly half, CHF 38.50; under-6s ride free. Valid one day on any train along the route. Supersaver tickets are yield-priced and not shown here.
Luggage. Mainline Swiss trains: racks and standing space by the doors; bicycles need a reservation on this train.
Hours. The IC81 leaves Zürich Flughafen at :46 every hour from 06:46 to 18:46 — 13 trains a day, each taking exactly 2 h 13 to Interlaken Ost, no change. Earlier or later than that, every itinerary sbb.ch offers involves a change, typically at Bern.