Do you know where in Lake,Bled to rent a car? I want to drive through Istria and return car to Ljubljana.
I don't know whether there is a rental agency in Bled. Even if there is, it would be worth comparing prices for pick-up in Ljubljana, which is a pretty short bus ride away and not even exorbitamt by taxi (as of 2015).
I've never rentednin Europe myself, but the usual recommendation is to start with the consolidators, who often have better prices than you'd get by working directly with a rental company. Names often mentioned are AutoEurope, Kemwel and Gemut.
Google Maps shows Bled locations for Europcar, Budget, and Avis, which may all be represented by AutoEurope, as well as a couple of local agencies. If it happens that you have to go to Ljubljana for a particular size of car or automatic transmission, then I'll second the motion that the bus works fine to get there.
One way rentals (within Slovenia) may not incur an extra drop-off fee as long as you rent the car for a minimum number of days. Note that some agencies will charge you a fee for driving into Croatia. All car companies have different policies.
I recently rented from Avantcar in Ljubljana, for a day rental also returned there. No idea if they have an office in Bled. They were OK, I'd rent from them again. In the past, I've used EconomyCarRentals (a broker) to find a good price on a car rental in the region.
We picked up a car in Lake Bled and drove through the Julian Alps and returned the car in Ljubljana. I can't remember if it was Budget or Hertz. There is no office there but they dropped the car off there at no extra charge (which we almost thought was too good to be true!). This was in 2015. Enjoy your trip!