I've flown into Marfa many times. They do have a crew car and they hide a key to the room where the crew car keys are in if you need it after hours. You can't reserve the crew car, but call the FBO and they might tell you how to get the keys if you're going to be there after hours. There is also Tipsy Taxi 432-294-0990 that I have used. In a bind, I've gone out to the highway and paid a guy $20 to give me a ride into Marfa and back to the airport.
If you need hotel or restaurant suggestions, I've been to a few.
Unrelated to your question Marfa story:
I got my instrument rating at American Flyers in Addison. American Flyers had framed letters in the hallways from former students telling American Flyers how thankful they were and what great flight training they received there. One of the letters was from the CEO of Western Sizzlin and he included a picture of him leaning against his Ferrari Mondial in front of his Cessna 182 RG and I'm sure he thought he looked really cool. With that in mind, I told my wife to take picture of me in Marfa with the crew car so I could send a similar letter and picture to American Flyers. I still haven't typed the letter, and probably never will, but here is the picture: