Trying to get to Valencia

Hi all,

Im trying to get to Valencia, but Interrail (mostly eurostar, tgv and inoui )are making it very difficult and expensive for me.. 

I want to get from Rotterdam to Narbonne on May 31st, and then travel the next day to Valencia. The first day is the problem, especially the part between Bruxelles Midi and Montpellier (where i need to change)

For basically every option i see the pass is either not applicable or I have to pay a genourmous reservation fee (ie around 160 euro on top of an already pretty expensive pass). 

My ultimate route was: 

1. Rotterdam - Bruxelles midi 06:40-08:03 - no need for reservation
2. Bruxelles midi - Montpellier Saint Roch 08:17-14:30 - IMPOSSIBLE
3. Montpellier - Narbonne 14:50-15:53 - 10 euro reservation 

The only affordable option is leaving Brussels at 14:00 and arriving in Narbonne really late (around 22:00), which kind of defeats the purpose of the journey. Can somebody help me get an alternative route? Otherwise I'm afraid I have no choice but to take the plane….