You can build one yourself for that price that'll be better suited for the needs of unraid. All you need is a motherboard, processor, ram, power supply and a case. Plus hard drives obviously. The power supplies that come in those prebuilt PCs are also usually proprietary and very cheap and won't be able to handle it when you add more than just a couple hard drives. Take a look in the good deals section of the forums for good deals on the components you need to build your own. If you get the components shipped to your house you can have it put together in the amount of time it would take you to drive down to Best Buy to pick it up and bring it home. Putting a computer together is really easy.