A year or so back, our family decided to built a joint family home over there...not too lavish, just something simple and comfy. Did alot of recce and all, Nathiagali was a bit expensive...(I don't remember the exact numbers right now).
Then the off road places which were a bit cheap but were lacking the basic facilities like water, phone etc. So you wold have to do some extra investment.
The places we found most suitable w.r.t the cost and facilities were near the old road to Murree. You know that famous mosque near the stream...one house was near that...and another one was near the Army Artillery unit just at the beginning of the road while going from isl to Murree...
Decent cost, facilities also available, weather also pleasant...especially near the mosque.
Another place you may try is near the new expressway, I reckon it would be cheap now and later it would rise sharply...Bahria Town's golf resort is also coming up there