But it is kind of "strange" question.
In 2016 I spent 1,5 month in Greece and make a lot of long trips.
So on engine "clock" was 1700 liters and 113 hrs.
This year it was 4 weeks, 60 hrs and 800 liters. We made only few long trips and usually go every day for Islands not very far away like 25 km.
If you go to Croatia to Murter Island (no need for ferry there is bridge) the trip from Tisno to Kornati is about 120 km whole trip.
It is your choice if you make many long trips like to Pag island or to Hvar (120 km one way) or you just wander around Murter and around other island.
You can make trip to KRK waterfalls which is mostly limited to 10-12 km/hr (channel to Sibenik and river and lakes) and you spend less fuel than on the fast cruise.
So fuel consumption is on your hand depends what kind of activity you choose. In Croatia you have many small islands in close range so you can enjoy them not going far away.
About road trip just use google map to check distance and fuel consumption depends on your car. Average price for petrol Austria 1.5 / Croatia is 1,3 EUR per liter
Fuel-prices-europe.info - Current Fuel Prices in Europe
In Greece municipally marinas are usually for free and you don't need to pay any fees and don't need to register at port police or coast guard.
In Croatia you have to show
- boat registration
- boat insurance
- drive boat licence
To pay for use boat (vignette)
but in my defence as driver he did say go faster so I obliged of course 25 kn stuck in a turn he was nearly passing the boat at one stage 
Matchless
one rule of boating I've learnt better to have it than be looking for it 
