Sounds reasonable - Rs. 30K for round-trip by private car. I assume that it for Corolla
Even if we have a look at some cheap tour packages (Facebook is bombarded with ads'); they charge avg. Rs. 25K (per person), which includes shared transfer (presumably by a bus/ coaster) and accommodation also. For a couple, it totals to Rs. 50K.
Having said that, if we exclude the accommodation factor roughly 30K for 6-nights that also leaves us with Rs. 20K for transportation (i.e., Rs. 5K difference per passenger).
Now Rs. 5K extra is worth paying for a private transfer where we can exercise the liberty of stop and stay where desired and a far-better comfort level than a shared transport.
I am not sure about NATCO and others as to what they offer. But given the 16-17 hours travel required from ISB to HUNZA and other way-round, I would not compromise the comfort to deteriorate the overall experience.