I'm very experienced with charter in Croatia. I can help you if you wish, just write me an e-mail at joseph.novak AT seznam DOT cz.
As I've read the post above -- it's not true that you MUST spend a night in marinas. There are lot of buoy areas and bay where you can stay. Charter in Croatia is quite cheap and if you select proper charter company you can get good quality as well. The bad news is that you have to book yacht long time before you start since a lot of people is chartering there from all over the Europe (especially if you want to go for June -- September).
Another problem is that you will not get quality in every Croatian charter company. They are sold very soon so a lot of them do not care about the quality and clients. Write me an e-mail and I can send you more information.