Montenegro is actually a brilliant place to drive around, the country is tiny, so you can go from the beach to the mountains in under two hours, and the scenery along the Bay of Kotor is absolutely stunning. The rental scene is mostly local operators, which means lower prices than the big chains, but you definitely want to book through a platform that shows the real total cost upfront. To rent a car in Montenegro, you can check out what is available here
https://getrentacar.com/en-US/montenegro .