Would you drive or take train from Paris to Switzerland/Interlaken?

Pete, I will try to chime in again (usually I don't, but you put a long effort in making your doubts clear and objective and asking for input, so here I go): 1- to get accurate estimates of toll costs (and a 'best-scenario' driving time - excluding traffic jams or any slowdowns or stops), I recommend the ViaMichelin website (viamichelin.co.uk). Click on the British flag for a better English version if they stick you with the French one. In your case, it might be anything for € 12 to € 31 depending on your route. Add CHF 40 for a year-long sticker for driving a foreign car in Switzerland 2- just a matter of market forces and some taxes. I currently live in Netherlands, close to the Belgian border. If I rent a car (prefer to rent a bigger one for long trips), I go across the border and save usually 30-40%. 3- Train schedules for June will not be released until late April. But they are unlikely to change much. Don't use RailEurope, that website gives higher fees. Check train schedules for that route on tgv-europe.com (use the British option again) 4- No 5- On international and high(er) speed trains, that is usually the case, indeed. But bookings only open 90 or 60 days before actual travel date. ========= Considering your overall route, I'd do short-term lease of a car in Paris, with Renault or Peugeot (they have dedicated sites to this mode of rental). These leases are, for practical matters, rentals (which must be arranged well in advance while you are in US by an US agent for them) from 14 to 180 days, in which you get a brand new car with special plates (reds), all insurance and roadside assistance included, and with far more reasonably international drop-off fees. Considering your other posts, this is what I'd do in your place.

I have just checked the journey options using the SNCF website at http://www.sncf.com/en_EN/flash/ and saying I lived in the United Kingdom. I chose a date in March. There are trains every two hours and one-way fares for an adult start at £67, which is about $100. That fare is for the 0823 train. The 1023 train costs £82 ($125). Both trains require a change at Basel, and the journey takes 5 hours.

I think Andre has a good suggestion with the lease. I leased once through Auto Europe, and it was a great experience. I needed a larger vehicle, so I got a brand new Peugeot minivan. If you pick up and drop off in France there is no additional charge. I picked mine up in Frankfurt, so I did have to pay a little extra. When I did my lease (5 1/2 years ago) there was a 17 day minimum. I actually turned mine in after 15 days because I no longer needed it and didn't want it in Paris. Advantages of a lease - Pay in U.S. dollars, so you don't have to worry about changing exchange rates. No hidden fees or taxes. What they say it is, it is. Roadside assistance (never needed it). All insurance included. New vehicle, exactly what you order.
I believe our only limitations were not to drive it in Eastern Europe.

Did you check to see if budget air flights are available? I'm not sure which airport would be convenient in Switzerland but it's geographically a small country with pretty good public transportation.

What would I do? Train. Rule # 1 is don't use RailEurope for fares, routes, or schedules. As Bob stated, the journey from Paris to Interlaken Ost takes just a wee bit over 5 hours, with a single change at Basel. Very easy. While you cannot yet see actual schedules and fares for late June (due to a Europe-wide schedule change in mid-June), they will change very little from what they are now. Fares do not go up in summer, and they don't bounce around like airfares. You should buy train tickets on the various national train websites. Often there are discount fares for advance purchase (a month or two ahead). For Paris to Interlaken, compare prices on the French site (SNCF) and the Swiss one, SBB.ch or rail.ch for Englilsh. I find the Swiss site easiest to use; you don't have to pretend to live in the UK to avoid getting switched to RailEurope. I chose a random date in March to check prices on rail.ch. Standard full fare from Paris to Interlaken is 187 CHF. Special offer price, 134 CHF. If you have a Half-Fare Card, the price is 107.50. If you are doing any high-mountain lifts or trains, such as the Jungfraujoch, you will want a Half-Fare Card for each person 16 and older. With that, you can request a free Family Card, and any children 15 or younger will be FREE on all Swiss transport so long as they travel with at least one parent. If Italy is your next stop, you can also get deep discounts on tickets from Luzern to Milan (around 25 CHF instead of 86 last time I checked). Then pick up your nxst rental car in Italy and avoid inter-country drop fees. If Germany is your next stop after Luzern, you can find similar discounts for travel to the major cities (Stuttgart for example).

As Bob from Bristol said, you can get discount fares for Paris-Interlaken by booking in advance (up to three months allowed) at either voyages-sncf.com (in French) or tgv-europe.com. To keep the tgv site in English and to avoid being bumped to the Rail Europe site which doesn't offer discount fares, choose Great Britain as your ticket retrieval country. Don't worry. You will be able to pick up your tickets at any SNCF station in France. The fares do not increase during the summer, but there is an allotted number of discount fare tickets for each departure date and time. When the cheapest tickets are gone, the fare increases to the next level until all that remain are full fare tickets. The cheapest fare is €72.40 which is the total of a Piccolissimo fare ticket from Paris to Basel and a standard fare ticket from Basel to Interlaken Ost.