@heychirag Based on your requirement I think TP Link Archer c7 is ideal fit. It's available on Amazon.in for 5500/-. This is the cheapest dual band gigabit router with openwrt support with decent cpu (750mhz) which will give you at least 200 mbps, if not more. If you want further lower cost, look for archer c60 at 2500/- but it will not exceed beyond 100 mbps.
I use luci-app-mwan3 mostly as fail-over (one of the ISPs as only backup/standby mode) on this, it works absolutely fine.
Also integrated dual-band wifi.
Only drawback i believe still exists: No support of mwan3+fast-path. Lack of fast-path means speed won't reach gigabit, even if you have it from ISP. I have seen speeds peaking between 200-400Mbps.