What is your definition of cheap? Don't rule out ARM based solutions.
However, the poor I/O capabilities of most/all toy SoCs rule use as a high-bandwidth router out; you can't do Gigabit routing with just one built-in MAC and the other connected to a USB 2.0 port or somesuch.
It sells for $49 on Amazon. https://www.amazon.com/dp/B06Y3V2FBK
AES-GCM runs quite well on ARMv8:
https://www.rsaconference.com/writable/presentations/file_up...
We have a 3 port ARM board (one port has a switch on it) being announced on Thursday.
[0] http://espressobin.net/wp-content/uploads/2017/01/ESPRESSObi...
I'm certainly not ruling anything out. I simply want to be able to get a working PFSense instance up and running.