I would like to find a way to depart from Dubrovnik, cross over the border into Bosnia-Herzegovina and rent a car for travel to Mostar and on to Sarajevo in September. I am looking for suggestions on locations and rental companies close to Dubrovnik while avoiding cross border drop off costs.
I don't have rental car suggestions, but to offer another alternative that is cheaper and stress free....just take a bus. I recall the bus stopped at Ploce, Croatia and then continued on to Mostar. I believe I took the train from Sarajevo to Mostar (this was in 2011), but I'm sure that a bus is a possibility as well.
I took the bus directly from Dubrovnik to Mostar, which included one rest stop near the border crossing. It was easy and relatively inexpensive. Only small disadvantage of bus versus car was that I had about a 15-20 minute walk from the bus station to my hotel near the bridge.