1.Cheapest option would be change the existing antennae of your router with a high gain one , if the antennae is removable.Should cost you around Rs.400-700.
2.You can get a wifi range extender. TP-Link range extender is available around Rs.1600,then you have Netgear WNR2000RPT around 2500.
3.You can replace your existing wifi router with a one with better range. Would cost around 5k for a good range one.
IMO option 2 is the best. I am using the same setup at home and it works seamlessly.
^^Wireless N doesn't necessarily mean higher range, means higher speed.