What is a good cheap 2 ethernet port SBC

I'm not sure about "good", but for "cheap" take a look at the Orange Pi R1:

https://www.aliexpress.com/store/product/Orange-Pi-R1-H2-256...

http://www.orangepi.org/OrangePiR1/

As far as I know, OpenBSD is supported[1] on Ubiquiti EdgeRouters[2].

Depending on what you need, a readily available appliance at a reasonable price (~$100) might even be better than just a SBC.

[1] https://www.openbsd.org/octeon.html

[2] https://www.ubnt.com/edgemax/edgerouter-lite/

The fli4l community looked into different options and I have heard they often use ALIX boards[2] with up to three ethernet ports.

[1] http://www.fli4l.de/en/home/whats-that-fli4l/

[2] http://www.pcengines.ch/alix.htm

Yep, I can vouch for the pcengines boards.

I have experience with PC engines boards in the past. They are good quality but the price is about 5 times what I am looking for, e.g. something about $20-30 to build a competitive network appliance with.

I am looking for something about $20 to $30 per unit.

What is an SBC?

Oh nevermind single board computer.