I too like djp_syd's plan.
No way fly from Paris, the High Speed train is faster and more comfortable. It is called "TGV-Lyria", click here for the timetable.
For train times and prices within Switzerland use the Swiss Railways website: http://www.sbb.ch/en/home.html
If I had to skip 1 place, I would Skip Geneva and leave in Bern. You could stop off in Geneva for ½day on your way from Paris.
You could also do Bern as a day trip from Lauterbrunnen.
When travelling from the Berner Oberland to Luzern, take the direct-but-slow train route via the Brünig pass, scenic.
A recommended day trip from Luzern is Titlis. It is a mountain with a permanent snowcap and a small glacier at the top, which you can go to the top of via a series of cable cars. Details here: http://www.titlis.ch/en
As a Swiss resident, Switzerland is not expensive, the rest of Europe is cheap :-)
P.S. Investigate getting a Swiss pass or a half price ticket for Switzerland, this will almost certainly pay off, especially as you will almost certainly go on a number of mountain railways and cable-cars.