dual gpu - sorry, no dual gpu under low/medium category. [only above 30k & for nvidia, cost additional]
Now a days no one consider dual gpu except miniers, ai based 3d design, 3d server etc. Better to buy a extreme end gpu than dual gpu. low cost dual gpu works on half bus speed, and single gpu is better than dual in this case.
cheapest mobo can't fully support 7900 and cause issue with 7950x, and
cheapest mobo which fully support cost around 25k and dual gpu cost around 30k. Mobo cost around 35k[best] to 80k [extreme] for 7900/7950x, now threadripper cost around 45k to above 1l.
X670 for r7/r9. very expensive 25k
B650 for r5/r7, less expensive 10k
both am5 socket, under 80inr per $
When processor speed, power, price increases, same goes to mobo, don't put a race car engine [2k~3kcc] into nano, r7 user buys mobo around 30k and r9 user around 40k, and if you want rtx3090/4090 gpu, better consider mobo around 30k~35k. or consider r5/r7 with mobo around 15k/25k with rtx4070/80.
Mobo & cpu just the first part, then atx[4000], cooler[5500], smps[7k to 12k modular], ups, ssd [5k to 20k] list goes on.
In simple if i3 gaming system cost x, then i5 - 2x. i7 - 4/5x, i9 - 6.5/8/10x.
i3- fhd gaming, i5- fhd ultra, i7- 4k, i9- 4k ultra. [nvidia fully support led display cost premium]
5 years back you can buy r9 mobo around 15k, now 25k.
how much mobo cost you expect for r9/r7 ?