In three years, there will be a very significant increase in prices due to the expected completion of margalla avenue and possible movement on motorway interchange. Also, the new airport (even though far from b-17) will push up prices in zone 2 generally.
Investment-wise, b-17 continues to remain a good buy for a 3-year span as it will likely experience a good value gain in that duration.
For building your house too, it is a good area because it is beautifully planned with a view of the margallas and it will be at a very convenient distance from islamabad - as soon as margalla avenue becomes operational.
For safe investment and good location, you can go for block c one kanal. C block is in islamabad capital territory. But if you can afford some risk (from time-factor point of view) you can go for e block but this block is outside islamabad territory.
However, if you want to be closer to the airport and kashmir highway of islamabad, then in your budget you can easily afford one kanal in e-17 cabinet society. In this choice (e-17) you will be able to save some money which you can invest in a small but potentially volatile investment like faisal town or small plot in pechs (when you want to build your house - you can liquidate the small investment and you will easily have enough money for constructing the upper storey and perhaps boundary wall. Right now e-17 is cheaper than b-17 block c, but it will cross b-17 block c because cabinet is very near f-15 where the price of one kanal is above 1 crore.