In September 2014 we rented through AutoEurope, and received a car through "Fleet" rentals at Dubrovnik airport (picked up there and dropped off there). It was CDN $110 for 4 days, plus a cross border fee of EUR 62,50 including VAT for going into Montenegro and Bosnia.
We stayed at an apartment in Cavtat for our time there and the airport is very close to there so it was very convenient.
No real problems at pick up or drop off. At DUB airport all of the rental companies have little booths all in a row along a sort of sidewalk, out in the rental car area. Seems like they are all run by teenagers. The place is packed with cars and there is very little room to move around. Early morning dropoff was particularly crazy. Lots of other people dropping off at the same time and everyone was just leaving their vehicles wherever the was a random spot. I can't imagine how they sorted it all out later.
Short walk to the terminal from there.