Where to buy Swiss Vignette

Buy it online, but only on the official website. Start here, read the information about the numerous attempts at fraud, and only use the link provided: https://www.bazg.admin.ch/bazg/en/home/services/services-individuals/strassenabgaben-private/vignette-autobahngebuehren.html

You need the car's registration number. And check beforehand whether the rental car has a Swiss vignette—unlikely in France, but worth clarifying.

You can just buy a sticker at the bordercrossing Customs St-Louis Highway https://maps.app.goo.gl/wpPgETbpGACzbb7T6

At the last gas station before the border.

There is no gas station on your way between the airport vehicle rental location and the border crossing.

Sorry for being obvious, but can I suggest you just rent your car from the Swiss side of Basel-Mulhouse-Freiburg Airport? Your car will have the vignette, and then you take a dedicated road to Switzerland without any further border controls.

Renting a car in Switzerland, especially if you plan to drop it off in France is going to be significantly more expensive.

Renting a car in Switzerland, especially if you plan to drop it off in France is going to be significantly more expensive.

That's usually true, but wonder if it applies at the very special case of Basel-Mulhouse-Freiburg airport, where the airport is actually in France (just "in Switzerland" for customs purposes). Interesting question.

When I watch travel vlogs, there is always somewhere at the border to buy the vignette. There has to be.

There is a customs station on the highway from the airport to Basel, and you can buy a vignette there.

In high season, there are usually customs agents in dedicated lines, selling vignettes. In low season, you just stop at the border station (plenty of parking) and go to the office to buy the vignette.