In reply to tkenopic:
First, full of envy for your trip. This is just some thoughts:
- As you get closer to winter, the eastern mediteranean tends to be wetter than the west, I'd therefore think of turning the trip the other way round.
- as you are clearly out of the main holiday season, I'd suggest a combination of small car and camping gear might work out reasonably cheap. This also gives more flexibility regarding visiting cities and not to pack everything in the.morning.
Several places allow for cheap or free camping (especially in spain, if you are discrete). In addition, the money saved can easily be invested in a gite / hot shower for a day or two. These options should be plentiful in off-season, but a night for the whole family would on average probably come around 50 EUR.
Not sure if flying Rome - Croatia and Croatia-Greece does make sense. Either car (1day) or ferry would be equally possible ...
... should Kaly be part of your plans, forget about a car there altogether.