The ampie case itself is cheaper. The product specs suggests that the Opus is using the Morex 3688 case, but it looks like the Opus Mini-ITX which is $379 compared to the ampie's $80.
Reasons for the cost difference:
- Opus is a better power supply and probably provides more watts
- The Ampie doesn't allow PCI addons (I think) whereas the Opus comes with
a 2 slot PCI riser card (these aren't cheap either).
You have it so that they are building and testing the Opus, but you are building the Ampie, I think that's another $35.