As PFSense is pretty lightweight and doesn’t need QuickSync, any old SFF box would work, e.g., decommissioned desktops from doctor’s offices, etc. The SFF form factor is handy as it’s essentially a small 2U and has room for half-height / low-profile PCIe cards. Pick up a $10 I340-T2, pop in a small SSD, 4GB of RAM (most listings will include this), and your new router is ready.