In fact when I was travelling for my summer holiday in Bulgaria, I have chosen to go with a flight. I bought a cheap flight to Sofia, Bulgaria, then I rent a car by a company in there, I think the name was Veger Rent a Car http://www.vegercar.com/en - the prices were very low- I find this way of travelling much more reasonable, i saved a lot of money and also had a car during my whole holiday in Sunny beach.