Have you looked at the new Mikrotik RB750Gr2 as it uses a very capable firmware comparable to Pfsense.
Alternatively, you would need to look into what a certain build your own spec could achieve in for instance LAN to WAN throughput and see whether the cost is justifiable.
Also, if you had dual LAN you could add extra ports by adding a separate network switch so the Pfsense router is just doing the routing. In this case there are a few more mobo's to choose from but I also think you need to pay attention to the LAN chipset vendor as some I think are supported in Pfsense and others may not be.
Jenway are a mobo manufacturer that can be looked at too as they do some small mobo's and some they do a daughter board to add 4 extra LAN ports. Sometimes these mobo's are the ones where the CPU comes already attached to the mobo so these are at the lower end of the CPU range which is where the performance might not stack up against simply opting for the Mikrotik route to start with at substantially less cost.