I started planning of this trip well before in August 2018. I booked flights in October (Qatar Airways BOM -> DOH -> MAD ₹75000 for 2 persons). I missed best offer of Turkish Airlines of ₹68000 due to delay in bookings.
Total Expenses per person -> ₹175000 (₹350000 for couple)
Hotel Bookings -> MakeMyTrip, Booking.com, Expedia.
Forex Card -> HDFC Forexplus MakeMyTrip is available for MakeMyTrip Customers at ₹0. It gives lounge access for twice in a quarter only at International Airports in India for free. I also had a Priority Pass which gives Lounge Access at all International Airports for free.
Sim Card -> I bought 2 Vodafone Sim Cards in Spain for ₹2500 with 10GB+5GB data and 60min+60min calling. These sim cards can be used all over Europe.
Visa -> For Spain visa visit https://india.blsspainvisa.com/ . Fulfill list of all documents. Apply for visa 2 months before your trip. I applied for visa on 8th Feb 2019 and received visa in 3 days. Visa Fees are around ₹12000 for 2.
Attraction Bookings -> Use Headout app for bookings of attractions in Madrid and Barcelona as these cities are available on Headout. You will get discount through cashback on every booking. I also booked few attractions from their official websites. You can also try Klook but I found nothing best than Headout (previously used for Dubai bookings).
Internal Transportation -> Use Flights, Trains and Buses to travel. I booked flights with Vueling and Iberia airlines. I used GoEuro (now Omio) app for these bookings. I also traveled by Renfe high speed train. I used Omio and Trainline to book trains. You can find more details below.
City Transporation -> For 2 people, be strict with timelines so that you can seamlessly use public transportation (buses, trams, metros etc. very cost effective mostly €15-€25 for 2 persons/day). We were 4 people so we used Public Transport + Taxi. Use Moovit app, it shows all public transportation routes, timings, stops etc. It is the best app. MyTaxiApp, Cabify and Uber are the apps for booking Taxi. You can get €5 off on MyTaxiApp if you have a promocode. Uber and Cabify also gives off on first time booking. So if you are buying 2 sim cards, you can easily get off on 6 taxi rides (total €30-€50 off). Add your credit card as a payment option and pay by app.