M920q/M720q tiny with a PCIe riser (10-15$) and you have a very capable opnsense/openwrt box which can fit 4x1Gbit/s or 2x5/10 Gbit/s port network cards.

I run it virtualized (easier for backups/rollbacks) on mine with PCIe passthrough of the network card, sips power and is rock solid.