We left Puerto Rico for several weeks this summer. Parking at the San Juan airport that long would’ve been crazy expensive. We used the Sultana shuttle service from Mayaguez to SJU airport. $175 cash will take you door to door privately (not picking up anyone else). Totally worth it.
They give you a number to call when you land, they pick you up and off you go home. But brush up on your Spanish. They don’t speak English. (I totally had my neighbor call for me–yeah, it’s cheating! But what a Godsend!)
What I really liked was that the driver was totally willing to stop for a potty break. I had no idea there were public bathrooms on the side of the road by the tolls. Super clean and ACTUALLY had toilet paper. Unheard of!