Is MESH suitable for me?

Minimum budget upto 3k ...
Minimum? Budgets are usually conveyed in Maximum :P
If your maximum budget is anywhere near ~4.5k, then, as I said earlier, nothing would beat Deco M4 (2-pack).

If it has to be jugaad so be it
Connect your current Tenda AC router to the Jio router (via LAN cable - important) and configure it as an Access Point, place it on the other end of house. You'll have to keep on manually connecting and disconnecting depending where are you in the house and signal strength.

Don't bother with Range Extenders, Wireless Repeater Mode, and anything similar - as said by @kage they are neither convenient nor reliable.


Isn't the X20 a wifi 6 unit?
Yes, it says WiFi 6 on the official website.
 
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AP Mode (double NAT)
AP mode has no dhcp by default so no double NAT.

@proletariat You can look into routers with wds option. These can connect wirelessly to other routers & can work as range extender but with better performance. For example, you can buy one such router with wds & then connect it over wireless to main jio router using 5GHz band then can use its 2.4Ghz & 5GHz band for extended range connection. Only thing though, such routers with wds options are rare nowadays so most likely you will have to look into buying older used models.
 
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If all you have is an issue in a single room, there is no need for mesh - get a good WiFi AP (like from Omada), put in the centre of the house at the top most height you can.

Turn off the wifi on the jio box - possible to do by connecting to 192.168.29.1 and using the default credentials. its not possible from the myjio app

If you are using Jio (or Airtel) and with their router, best to put the WiFi AP in Access Point mode - this will allow you to use IPv6 from the main router. If you do double NAT or triple NAT - it just makes it slower. Websites on IPv6 are slightly faster on Jio - but I cannot put it down to IPv6 purely, it may be 1 layer less of NAT.