Although we planned drive ourselves in Croatia, we opted not to keep the car we’d rented in Montenegro for that trip. My reasoning was 1) we’d avoid cross border charges; and 2) we didn’t want a car for our days in Old Dubrovnik anyway since parking is nonexistent in the old town. The best option appeared to be a motor coach. I bought tickets ahead of time on GetByBus at https://getbybus.com/en/ for 483.5 Croatian kuna ($42.5o) for 2 tickets, tax included. A print-out of the ticket is required and the drive is about 2 hours. We had only one brief stop at a town along the way.