amazon.com has the Razer Core X Aluminum External Enclosure eGPU ATX Case (Classic Black) for $279.99 and shipping is free.

• External GPU Enclosure (eGPU), Built-In Power Supply (650W)
• Up to 3 PCIe full size graphics card slots
• Compatible w/ Windows (requires Thunderbolt 3 w/ support RS45 or later) (NVIDIA/AMD GPU)
• Compatible w/ macOS (requires Thunderbolt 3 and High Sierra or later) (AMD GPU only)