From what I see, the trip planner does not recommend an additional railpass. It appears to recommend that you buy some point to point tickets, including one from Paris to the border or all the way from Paris to Amsterdam. I see the trip planner recommends a 5 country select pass, but I don’t really think covering the countries in Eastern Europe with a railpass will be worth it.

Look for discounted fares at www.thalys.com www.tgv.com and on the French and Netherlands national rail company websites (links are here: http://www.eurotrip…. ) Pick France or UK for your “country” on the French and tgv sites to avoid getting switched to raileurope where you’ll probably end up paying “global fare” which is about 30% higher than standard fare. Make sure you can either print an e-ticket or that you can pick the ticket up (at an automated kiosk at the train station) in Paris. You will not be able to get a ticket by mail, or pick it up in Amsterdam!

If you can’t find a reasonable fare, then look for a cheap flight.

If you can’t find a cheap flight, then look at other railpass options. I’d look at having the pass cover France instead of Croatia if you’re looking at an expensive ticket between Paris and Amsterdam. Perhaps a global flexipass??

Buy Paris-Amsterdam as a point-to-point ticket. You can scoop those starting at mere € 39.

Book a high speed ticket in advance, that’s the most conventient way.
If you can’t get a cheap ticket, consider the bus, Eurolines can be very cheap when booked in advance (15 euros sometimes), but it is less convenient and takes longer.