X370 boards that i would recommend for R7 cpu's.
Highend:
1: Asrock X370 professional gaming.
2: Asrock X370 Taichi.
3: Asus Crosshair 6 Hero.
4: Aorus X370 Gaming K7.
5: Biostar X370 Racing GT7
Midrange:
6: Aorus X370 Gaming 5.
7: Asus X370 F Strix.
8: Asus X370 Prime pro.
9: Asrock X370 gaming K4.
10: Asrock X370 Killer sli.
I suppose that you could find one of those for the right price.
The midrange boards are basiclly all good enough for R7 cpu´s and overclocking.
The Aorus X370 Gaming 5 is the best board from the midrange list in terms of vrm implementation.
But those other midrange boards are also fine.