Buying a new pc for mount and blade 2: bannerlord help needed.

[caffeinade]

R5 1600 (includes a decent cooler)
$210

16GB Vengance LPX RAM
$150

EVGA 1060 3GB
$215

Corsair Carbide 270R + 500W PSU
$100

Samsung 960 EVO 256GB
$128

WD Blue 1TB
$46

Asus Prime B350M-A
$70

Total $919 USD

You can cut back buy buying a much cheaper case and / or not buying an SSD (or get a cheaper SSD).
Cheap SSD $54
If you have no intent to ever overclock you can buy a cheaper motherboard.
If you want to play games at a higher res (1440p or maybe 4k) maybe look at getting a RX Vega 56, GTX 1070 or better.