Go with cheap motherboards or used motherboards to cut down cost limit, days ago I ordered for a colorful mining motherboard at 100$ with 8 pcie slots but I already have a working CPU on ground, it's a AMD motherboard though
For mining, there is no difference on which chipset the motherboard is made.
Will write your motherboard model, I want to read reviews.
I like these motherboards because they can be used for both mining and building a personal computer, unlike the BTC-D37.
This is a compact solution for 7 video cards.