A fun project that results in a unique and stylish router is repurposing a Mac Pro Trashcan. They can be picked up for a few hundred dollars, offer dual 1GbE Intel NICs that work natively on Linux, and have plenty of CPU and RAM overhead. Throw OPNsense on there and you’re off to the races.
Performance per watt is not ideal on the trash can. But totally doable.
The idle power usage on those is atrocious compared to say an Intel N100 or an Arm system.