If you need multiple Supermicro Caddy´s this might be interesting at roughly 2,5€ per caddy.
144x Supermicro mcp-220-00075-0b 3.5 Zoll Hot-Swap Black Gen 5.5 HDD Tray Caddys | eBay
144x Supermicro mcp-220-00075-0b 3.5 Zoll Hot-Swap Black Gen 5.5 HDD Tray Caddys | eBay