What are the best options to travel by train from Lyon to Aix en Provence and pick up rental car? When I search for picking up rental cars in Aix/TGV, I get directed to picking up a car at MRS/airport. What is involved in getting from Aix/TGV to MRS?
Where are you searching for rental cars? Last I knew, there were several rental car locations at the Aix TGV station. Try AutoEurope (www.autoeurope.com) or the SNCF Avis partnership (https://www.sncf-connect.com/en-en/train/train-services/train-avis).
There are many rental car agencies at the Avignon TGV station. What may make sense is to take the train from Lyon to Avignon TGV. Pick up the car there and then drive to Aix. The train between Lyon and Avignon takes a little over an hour. While the drive from Avignon to Aix is longer than from the airport, this should save you some time over going all the way to the airport.
p.s. Just saw JHK’s post. His suggestion makes more sense if you can find a car at the Aix TGV.
All the major car rental offices are present at Aix TGV.
However, you can find cheaper deals at the airport: if the savings are 100€ or more, you could consider getting off at Aix TGV, taking the bus to the airport (15-min ride every 30 min, negligible price), and renting there. You'd waste an hour at worst.