Question best budget cpu for crossfire rx 580

[Usernamejimmy]

hi I need help im looking to do a crossfire set up with two rx 580 however I need help deciding the best budget cpu with this set up that won't cause crazy bottleneck.

 

[Gam3r01]

What is the purpose of this system? Budget? Any existing hardware?
Chances are Xfire is going to be an absolute waste of money.