Travel from Barcelona to Provence

Will you need a car in Provence? If yes, I would either take the train into France and rent the car in Perpignan, or train all the way to Provence and get the car there. You are correct that it is expensive to rent in one country and return in another. If you won't need a rental in Provence, just take the train to your destination.

We will be doing this in reverse: turning in a lease car at Marseille airport after 9 days in a gite and flying to Barcelona and then Barc to Paris. We're trying Vueling Airlines; their prices, even after charge for extra bags AND to pick seats, are way better than Iberia, Alitalia or Air France. I didn't check out the train and it wld depend on where, specifically, you're going in Provence. Yes, the charge is HIGH if you rent in one country and drop in another. We were originally going to do this but rethought it after seeing the cost and are leasing but picking up/dropping off car in France. We are leasing because we will have the car for 29 days (more than 17 days is less expensive than renting).

Where is your Provence base? Avignon, Arles ??
There are several high speed services per day from Barcelona to Montpellier, Nimes and Avignon.
A lot of Provence is accessible by train and local bus - to save costs consider a rental for only part of your week there. Return the rental in perhaps a different centre (Nimes or Marseille) and TGV to Paris.

We are starting our vacation in may in Barcelona, then we are taking a train across the border to Perpignon, renting a car, spending a couple days in that vicinity, then driving to Provenance and dropping car in Avignon before taking train to Paris. We found a rental (mini) for 9 days from Auto Europe for $150 with no drop fee.

Thank you all! Definitely taking the train and renting in France as we will need a car.