rent a car or other options from Ljubljana to Dubrovnik
 

We will be traveling next Sept. and I'm trying to figure out the best way to get to various spots. After traveling through Switzerland (by train) and Austria (car rental, returning it before going from Salzburg to Ljubljana), we want to go from Ljubljana to Plitvice Lakes, and then on to other stops in Croatia before ending our trip in Dubrovnik.
Renting a car in Ljubljana and returning it upon arrival in Dubrovnik (so we don't have the car in the city), seems like the easiest way to go. We like the idea of being able to stop along the way. We plan to go to Krka, then to Split and do some day trips, perhaps to Zdrilca Island/Hvar, Zlatni Rat Beach, if this can be done in a full day, or a kayak trip to Ciovo Island. (If anyone has suggestions about this, I would greatly appreciate it).
We will then spend a few days in Dubrovnik, taking in a day tour to Montenegro.
I know there is generally a huge drop off fee if we rent a car in one country and return it in another. We'd like to avoid this, but I can't seem to figure out where we would rent a car in Slovenia and return it there, then get to Plitvice Lakes without a car, and then rent one ther (if they even have car rentals there).
I'd greatly appreciate any helpful hints on how to make this part of our trip work. i heard that Idealrent car company is great, with no hidden fees. I went to their website and they don't post prices. Since we don't have exact dates yet, I'm hesitant to contact them (they ask on their website for me to put in my dates). Thanks again for any help!

From Ljubljana, take a train to Zagreb and rent the car there, then drop it later in Dubrovnik. That's the typical way people do it - the way I did it years ago on my first trip to Croatia. Rent a car in Slovenia for a few days if you really need one there; you don't need one for Ljubljana and you can take a bus to Lake Bled, but it is nice to have a car to explore the beautiful scenery nearby, in the small towns, and up over the Julian Alps loop, etc.

You might keep looking for companies that don't have those steep drop fees. Someone claimed that the company Sixt had modest but affordable one-way drop fees for these cities, but I have not checked or compared rates myself.

I agree with Andrew that it would male sense to take the train from Ljubljana to Zagreb and pick up a rental car there. But I would return the car as soon as possible after visiting the Plitvice Lakes National Park. Buses in Croatia are comfortable and convenient, and they allow everyone to enjoy some truly spectacular scenery, much of it from roads that require the driver's full attention.

Without knowing your time frame, I don't think we can comment on your itinerary.