Sorry for late reply. I just came back from Swat and Kalash (Chitral) trip last night.
We rented an XLI from Islamabad for Swat and Kalash trip. For Swat it was ok, however, for Kalash I wouldn't recommend you to take your own car as Lowari Pass is car crusher type of place. We were 5 people with lots of luggage, its bumper, body got touched million of times. After Lowari pass mistake, we took our car to Bamburet (Kalash) which was another mistake.
The best way would be to take your own car till Dir Bala city (Upper Dir), park it there in a hotel and hire a taxi from there which takes 800 per person or 3200 for whole taxi which will take you to Darosh (other side of Lowari Pass). Add another 300-400 and it will take you to Ayun turn (from where the way go to Bamburet, Kalash). From Ayun turn, you can hire a taxi which take 200 per person or 1200 for whole taxi which will take you to Bamburet.
While returning, we used taxi to distribute luggage and persons, then it was a bit easier journey on Lowari Pass. Otherwise, taking your own car is not recommended at all.