You don't necessarily need a router when taking a Jio Fiber connection bro. They provide a 5 Ghz WiFi enabled device. Connection (wiring etc.) charges are also included with it, i guess.
You need nothing extra other than a computer or mobile to connect to the internet.
Reliance wants more wired customers, so this offer is to lure customers from other providers. Without competitive pricing, they can't make that possible.
Even my ISP (Railwire) charges ₹4000 for installation.