If you can splurge a little, this little guy is awesome and includes support from the pfSense team:

https://store.pfsense.org/SG-2440/

Or you can buy one of these and flash it to pfSense yourself:

http://store.netgate.com/ADI/RCC-VE-2440.aspx

Cheap fanless motherboard with 2 NIC's: https://www.amazon.com/gp/product/B006ICQ3FK/ref=oh_aui_deta... ... pay attention to the power supply brick, you might need a little adapter dongle for the mobo.

and a cheap case: https://www.amazon.com/gp/product/B003DXI288/ref=oh_aui_deta...

No hard drive, just a usb stick to boot the OS off and save his settings. PFsense in my case, a BSD variant.