There is a limited 10€ fare and then it increases to 20€ per person (same price in both classes).

Everyone wants to leave Paris on Friday evenings so trains are expensive around that time. It will also be French school holidays so more people than usual will be travelling.

EDIT : if you leave at 14:55 or 17:24 instead it will cost you 10€.

Thats great Thibcabe  .. My first few interrail bookings.. was just checking i wasnt doing something wrong.  Now I understand its peak time and easter hols season !!  Thx

It’s not yet Easter but ski/winter holidays instead (not everybody goes skiing ofc). But it’s true that Easter will happen early next year ! :)

As far as I know SNCF is the only company to offer reservations at 2 different prices.

Further questions welcome and enjoy your trip.