Help with Basque Country in Spain and France
 

We ( family of 4 -2 kids age 8 & 12 )will be traveling in March from San Sebatian to Bayonne and wanted to rent a car once we are in Bayonne. I've read that a bus is best but which one and from where specifically? Also , would it make sense to rent a car from the the closest rental agency once we are over the border? Or go all the way to Bayonne? So we can see Biarritz and other cities on the way to Bayonne?

That will be one leg of our trip later this year and although we are only two people, older but not that old tourists, we will rent a car, so we do not have schlep our luggage onto buses or trains.

Although we have spent considerable time in Spain and less in France, this is the first time we are making this we are going from Donostia to Bayonne and Biarritz.

We do intend on renting a car but I don't want to pay for the extra fees for picking up in one country and dropping off at another. Our final destination will be Toulouse at which point we fly out.

Not sure I understand the question. Do you want to see Biarritz or not? If so, then get the car once you're over the border. And don't miss St-Jean-de-Luz.

The Corniche Basque (coastal road) between Hendaye and St.-Jean-de-Luz is very scenic with bizarre rocks in the sea, so it makes most sense to right right after the border in Hendaye, if possible. Or, as second choice, in St.-Jean-de-Luz, which has a picturesque harbour with seafood restaurants and a pretty beach.