Any regular cable internet (RJ45 Input) router should work. They will use a fiber to ethernet converter device called Gepon. BSNL has been providing internet through LCOs (local cable operators) these days. They maintain the last mile connection.
I suggest you Dlink Dir 615:
D-Link DIR-615 Wireless-N300 Router (I have used this one previously).
It costs 849 and works for fiber broadband services. You can get speed upto 300Mbps according to your plan.
If need better ones, check:
TP-Link TL-WR841N 300Mbps
TP-Link Archer C20 AC750
TP-Link Archer C6 AC1200 (I use this one currently)
Any of the above router would cost below INR 3,000. BSNL people are overpricing these simple ones. Better to get them yourself so you can save some money.