The cheapest way I can think of is a used PCIe HBA card and some SATA power extension cables. Probably $50 or so to connect 8 drives this way.

If you’re set on USB you can often get 4 bay enclosures for around $100 or so, that would the way I’d do it. The downside of single USB adapters is the sheer amount of wires and power supplies you’ll have.