If you just want to make a return trip, have you looked into buying normal tickets? Check both DB and SNCF websites for the complete journey.

When comparing prices, don't forget to add obligatory reservations for trains from/to/in France.

As to the mobile pass, it only works on a mobile phone. If you're in Germany and want to buy an Interrail, just buy a paper one from the DB ticket office. You would then need a global version and the minimum is 4 days. Or alternatively a 3-day pass for France plus tickets to/from the French border.

It’s just that the prices for the individual trains are a lot higher than for the interrail stuff, even the global one. The interrail ticket global is 185€

According to https://www.interrail.eu/de/plan-your-trip/interrail-timetable?ol=STUTTGART+HBF+%28GERMANY%29&ov=008029034&dl=RENNES+%28FRANCE%29&dv=008747100&vl=&vv=&t=1640919600000&ar=false&rt=&tt=&mc=&mct=0

the reservations are like 23€.

The global interrail is 185€ so there and back thats 185+2*23= 221

A normal ticket from DB website is like 170€ alone, just to get there. Ridiculous.

Cheapest option would be 110€ there, which is just as cheap if i get same price on the way back but it’s way slower and includes a flixbus.

With the interrail i can take any train i want if i understand correctly, i just need to reserve seats.

Correct, but there's limited availability, so if you already know which trains you want to take, I suggest to book them now.

By the way, 185 EUR is the normal price, but there's currently an offer for 167 EUR (-10%), also available from the DB ticket office.

As you will realise, these are peak-travel days, and SNCF and certainly for the fast TGV charge quite high supllement also with QUOTA_that means its very likely the quota for your wanted trains is already taken or simply not put in at all. You can perhaps avoid this with using more local trains=means much longer time and more changes. Also cooperation between DB and SNCF is not very good and that means it may be cheaper to buy separate tickets-but then you face the problem of the eternal delays so often on DB and perhaps loose the 2nd ticket. These '’fahrgastrechte'’’where all germans are so keen on then do not apply. But with an IR you face in fact same problem.

To cut cost also look-if you are a bit open minded- at BUS, even for just part of the way.

There is just no way i can find anything cheaper in normal tickets, the 110€ one i mentioned is already with a bus part of the way.

Ticket prices are just absoiutely ridiculous, and the 31st is actually a day of LOW travel on average. the tickets back onm the 2nd are even more expensive were i to buy them individually, talking around 200€ here.

There is just no reason at all to buy tickets instead of interrail, with interrail its cheaper and you get more flexibility by being able to choose when you want to depart.

Does my Bahncard 25 help me at all with interrail or no?

That's because you're still quite late booking this trip. A few weeks in advance would have given lower fares.

Nope. But I must stress to book your reservations ASAP. The TGV/ICE trains from Germany to France have limited seats for pass holders and these are often sold out a few days in advance. French domestic TGVs have a limited quota for 10 EUR seats and after that it's 20 EUR and these trains can also be fully booked.

That's because you're still quite late booking this trip. A few weeks in advance would have given lower fares.

Nah mate, the prices are simply ridiculous. I checked for 21 January for comparison, and there the prices are still 100 minimum, up to 270€.

Again, with buses for part of the way. just looking at trains im paying at least 130€

There is no way tickets are cheaper. The prices are just insane, which i really do not understand at all. Driving a fucking car is cheaper than buying traintickets.

Also, in times of Covid i do not like to book tickets long in advance. last time i did that, i wasted a 100$ ticket because one of my roommates caught covid a couple days before the trip and we all had to quarantine...