What mobo to go with rx470?

A buddy of mine owns of a computer repair shop and he has quite a few rx470's and he is willing to give them up if I work 1 week at his shop while on vacation. When I say he has quite a few I mean 7+.

What mobo would I have to use to seat as many rx470's as possible?

Trying to get a somewhat decent gpu rig for xmr.

I'm looking for cheap but effective but I'll also look at any mobo as I do not have a limit.