You can get an PCIe HBA on ebay for $50-60 bucks and will allow you to connect 8 disks to a single system. Look for ones that specifically say they have been flashed to IT mode which will let the host system address the individual drives and enable you to use MDADM for RAID. My "Server" is literally just the old motherboard from my gaming PC with 4x 8TB drives connected to one of those ebay HBAs.