There is a bus from Trieste to Rijeka that is really cheap - that's what I did when I was there. Goes from the centre of one town to the other - takes a couple of hours.
You have a hell of a long way to go to get down to Dubrovnik - I was driving it, and I wouldn't have been keen going any further than Split. Split, btw, has very few hotels. Be warned. Stayed in some little island-town outside of there called Trogir, which was great.
Haven't been as far south as you are looking though, so can't help with that.