We will be getting the 2-day flexi pass to save on the trip up to Jungfraujoch. It will cost us around 124 Euros for the pass
Well, Swiss Railways (SBB) sell special discounted tickets called SuperSaver (can be purchased 14 days before the journey), in case of Zurich to Interlaken trip SuperSaver tickets start from just 24,6 CHF (app.20 euro) per person). Also can get one from Interlaken to lake Constance (meaning as a part of your Interlaken-Munich trip)
The trip to Munich will cost us 25 Euros.
Here meant paying for German part of the trip Interlaken-Munich, right? For Swiss one you intend to use the pass?
We intend to get the Lander ticket for a day trip to Neuschwenstein castle. Another 25 Euros each.
Why each? Bavaria Lander Ticket for two passengers cost 26 euro (when purchased online or via DB ticket machine)
On the 6th night in Europe after Munich, we will take a overnight bus to Vienna, arriving at 0600 for a day of sightseeing. This will cost 36 Euros.
Honestly, this is a bit rough, with rail options you can get discounted 29 euro (per passenger) tickets for fast (<4 hours) day time train
At the end of the day, we will depart for Prague by bus at 2240. We will reach at 0330.
Again, you sure you want to arrange the journey this way, especially since it will be second night in a row withou bed? Maybe more comfortable will be to catch evening train (discounted tickets from 29 euro per person) or bus and spend a night already in Prague. Or spend a night in Vienna and then take morning train/bus to Prague
Following that, we will depart for Nuremberg in the morning at 0700 by bus, and arrive at 1030.
Between Prague and Nuremberg operate couple bus companies (DB ExpressBus, Student Agency, EuroLines), so we suggest to you check all of them and see which one offers better fares for the time and date you wantl
Here is where we will get rent a car for 158 Euros (a person) for the duration of 6 days. During this 6 days, we will be spending time in Stuttgart and Bruges.
158 euro is obviously a good price, but an alternative for German part can be just to go with Lander Tickets and Quer-durchs-Land-Ticket/Schönes-Wochenende-Ticket