I hear the transportation experts would be able to suggest how to get the best prices on this route: Paris - Basal (spend a few days in Berner Oberland and then) Zurich - Munich.
This is for July, probably 27 July.
Topping for Lee and Tim to see.
You can buy the Paris--Basel--Interlaken tickets on sbb.ch without worring about getting switched to Rail Europe like the tgv site does. I saw a "Piccolo" fare of 97 CHF from Paris to Basel on SBB (or 142 from Paris to Interlaken), but I don't know if that's the best one out there.
Topping? Steve just posted 15 min earlier? Oh, well. Thanks.
Jesse, I really specialize in German Rail tickets. Paris-Basel, and Basel-Interlaken will be better handled by Tim.
It would help if I knew how long you planned to stop in Zürich. If you just meant it as a change of trains, or just a few hours to sightsee, if you go to the German Rail website, you'll find that they sell Europa-Spezial Schweiz fares for as low as €39 all the way from Interlaken Ost (with train changes in Bern and Zürich). (This is unusual because DB normally only offers these fares for single train connections to a station in Germany, ie, no connections in a foreign country.) If you just want to spend a few hours in Zürich, you can build that stopover into the ticket by using "Via: Zuerich". If you want to spend the night in Zürich, you can still get that spezial fare from Zurich to Munich.
I think given the time they have for their trip, they will want to go Interlaken to Munich without an overnight stop in Zürich, so that 39,00 fare for the whole journey is the better deal.
I thought the Europa-Spezial deals were only from Zürich, so this is good to know.
This thing with Interlaken to Munich is rather unique. I also found a Europa-Spezial fare once from Chur with a leg entirely in Switzerland.
You can also get Europa-Spezial fares from Paris to Basel as low as €39 pP. The trick is to put in Basel Bad Bhf as the destination. This is a German Rail Bahnhof in Basel Switzerland, a few km (streetcar) from Swiss Rail's Basel SBB Bahnhof. Because it is officially in Germany, German Rail sells Europa-Spezial fares from Paris to Basel Bad Bhf (actually Badischerbahnhof). The routes generally go from Paris to Karlsruhe (TGV), then an DB express train (ICE/IC) from Karlsruhe to Basel.
You can book Paris-Interlaken with a connection in Basel (Bale in French) on tgv-europe.com. If you book far enough in advance (up to three months allowed), you can get a Piccolissimo fare for Paris-Basel combined with a standard fare for Basel-Interlaken for a total of €58.60. The standard fare for the whole route is €128.60 so it pays to book ASAP.
To keep the site in English and to avoid being bumped to the Rail Europe site, choose Great Britain as your country of residence.