Which motherboard you want is a question X470, or x570 or B550 or B450,
I assume you would want a X570 motherboard means for your beefier 3900x, so the cheapest GIGABYTE X570 UD will cost you 273 Australian USD or 14281 INR, and the X570 UD is the motherboard i have where the BIOS can be updated VIA pendrive which does not require memory or cpu to be installed initially.
And if you want the cheapest B450 then Asrock B450 Pro4 will cost you around 139 australian dollars,
but with the Asrock B450 Pro4 motherboard you need to update the BIOS with a compatible CPU first,
i suggest you not to go for the cheapest mother for ryzen 3900x. So dont go for the cheapest motherboard for 3900x if you want to maximize the...