Istanbul is a bit expensive place
for 2 week it will aprox 40k-45k inr if you live in hostel and try to make it a cheap trip
like using public transportation instead of personal like taxi and al.
if you need any help feel free to ask.
Book hostels from booking.com you will get the price in cheaper rates and try to book hotels in sultan Ahmed area its is main tourist location where you can hotels in cheap rates
1)Check the flights on skyscanner.com
2)Check hotels on hotels.com/booking.com/agoda/expedia.com
3)For local sightseeing tours,check viator.com Flights would be around 30K (onward and return journey included).
Hotels you can take as per your budget.I stayed in Hotel Niles in Istanbul. Turkey is comparatively less expensive than other european nations.