lauterbrunnen to venice by plane

In order, the largest airports in Switzerland are Zurich, Geneva, and Basel. According to their Wikipedia entries, all of them have service to Venice (Zurich on Swiss, the others on EasyJet). To see which is easiest to get to, you would have to check the train links from Lauterbrunnen on Swiss Rail: http://www.sbb.ch/en/home.html. And to see which is cheapest, you have to look at Skyscanner: http://www.skyscanner.com/

While you're on the Swiss Rail site, I'd look into taking the train all the way. By the time you get from Lauterbrunnen to an airport (in time for check in), fly, then get from the airport to Venice (takes time unless you're splurging for a water taxi), you may do just as well to take the train.

rudy,

Basel-Mulhouse is probably the easiest airport to use from Lauterbrunnen and EasyJet will likely have the cheapest fares if you book well in advance. The travel time will likely be about the same, whether you travel by train or budget airline.

The shortest rail trip appears to be a departure from Lauterbrunnen at 07:03, arriving Venice S.L at 14:10 (time 7H:07M, 3 changes). Although the flight from Basel is only 1H:10M, by the time you include travel to and from the airports, security, waiting times, etc., it will probably be about the same time. Travel by train will be a much more pleasant and relaxing trip.

You're on the right track with the advice above.