Advice for last minute car rental from Paris to Pau

Why don't you look into flying. Weighing the cost of a rental car, two nights hotel, gas, tolls, it might be less expensive for the two of you to fly, even last minute.

I used to have family in Pau and the drive from Paris takes forever, about 8 hours.
NOT recommended, and costs about 400€ round trip for gas and tolls.
The plane is really the way to go: shorter, less exposure, better air filtering systems.

You need an IDP to hire a car in France - do you have one?

It’s a long drive and I would fly. If you do hire a car, getting an automatic maybe easier from Orly airport rather than hiring in central Paris.

Presumably you have taken some LFTs with you or can get some in France as a check before visiting your friend. My mum has COPD and there is no way I would want anybody visiting her that didn’t take a LFT just before the visit, even if double vaccinated. I always test myself when I go there for peace of mind.

The plane is really the way to go: shorter, less exposure, better air
filtering systems.

For Covid reasons, the train is the better option. Once you add all the airport faff (which tend to be indoors) there will be less exposure by train, where the station often are semi-outdoors. And while trains don't have as fancy air filtering systems, they don't need them because they don't reuse the cabin air.

I’ve rented cars in France 30+ times and have never been asked for an IDP (International Driver’s Permit). We were involved in a serious car crash in Sept 2019, 10 cops from different jurisdictions came to the scene and interviewed us, no one asked us for our IDP.

If you do end up driving, there are two routes. Via Bordeaux and via Limoges-Toulouse. It is about 1hr quicker via Bordeaux, but going down one way and up the other will help break the monotony! Paris to Bordeaux on the A10 motorway is especially boring...

ViaMichelin suggests three possible routes between Paris and Pau.

The western route is fastest. It skirts Poitiers, a city of 88,000 with a lovely upper historic district where I felt the only non-French person present in June 2019. Poitiers has some important early churches: a 4th-century baptistry (now a small museum), the 11th-century French Romanesque Notre Dame le Grande, and an early Gothic 12th-century cathedral. The route then passes Saintes, an attractive smaller town of 25,000. Then you have Bordeaux, which is larger (over 250,000) and takes more time to appreciate, I think.

The eastern route is the next fastest. It goes through Limoges (130,000 pop), which has a very pretty historic center and several good decorative-art museums. The route then cuts across the Dordogne and Lot, passing near a lot of places mentioned by visitors to that area. Two of the closest to the route are Brive-la-Gaillarde (47,000) and Cahors (19,000). The tiny spots like Rocamadour or St-Cirq-Lapopie would be a bit more of a detour. The route then skirts the handsome pink-brick city of Toulouse (470,000).

The longest route follows the eastern one as far as Limoges then cuts across to join the western route south of Bordeaux. On the cross-cut it passes through the handsome town of Perigueux (30,000).

As someone who has never had the benefit of a rented car in Europe, if I wanted to take some extra time on the trip, I'd spend it seeing some of the small villages on and around the Dordogne and Lot that are difficult to reach via public transportation.

Thank you everyone for your advice. We looked into flying to Pau but it turns out that it would cost about $400 per person round trip this late in the game. The idea of a road trip is really appealing to us because there is so much of France that we haven't seen but because of the length of the drive (8 hrs each way) and our inexperience with the roadways in France, we've decided that we'll save the road trip for next time and I'll train it to Pau alone, double masked with a cloth mask over a KN95. Jennifer, thanks for the LFT suggestion as I was planning on taking an antigen test which costs 29 euros instead of the 5.4 euros for the Biosynex one I just purchased from the local pharmacy. I can't tell you how much I appreciate the thoughtful responses from the good folks on this forum. Thanks again for your help.