France and Spain are the worst two Countries for rail pass travel - compulsory reservation for most trains you will take, and the reservations are pretty pricey.
Reckon on €10-20 for domestic TGVs in France, €10 for Intercity, €35 for the TGV to Spain. Generally, first class reservations for these journeys are the same price as second. Usually bookable online.
In Spain, it’s more expensive - €10-25 for anything other than a local train. Even most regional and local trains need reservations for a few euros, and they are difficult to buy.
Portugal is compulsory for the fastest AP and Intercity trains, but only costs €5.