For the i3 8100

[darknopror]

Best budget Motherboard
For coffee lake ( LGA 1151) ?

 

[PuperHacker]

Here is a list of cheap LGA 1151 mobos: https://pcpartpicker.com/products/motherboard/#c=129&f=2,7&s=30&X=0,7630&m=7,8,18,27. You could also go with the Z370 chipset, but these mobos tend to be more expensive.

 

[richiestang_78]

The MSI B360M BAZOOKA or for even cheaper the GIGABYTE H310M A

If it were me I would spend a little extra and get the ASRock H310M-ITX/ac and make a nice little ITX build.