Rawalpindi to Astore. big AC bus chalti ha. Bunji Astore road is usually open year round.
Yes Deosai full traverse is jeep trek. deosai k starting point tak car bhi ja sakti ha. (Upto Sheosar/Kala Pani) from Chillam. But can't go to Bara Pani.. and also can't descend to Skardu.
Individual person ka itna ziada nahi hoga. 100, 200 hi hoga.. (not a matter of concern)
Do google and get Hunza hotel phone, and get info for charges of car.
Jeep rent could be 20K for Skardu Rama and back.