I just got my pfSense running with the following hardware....
HP Prodesk 6200 i3-2100 with 8 gb RAM (came with an HDD I didn't use): $50 second hand from a private seller. (Just the box, no peripherals)
Two, TP-Link TG-3468 NICs (one for LAN and one for OPT); ~$12/ea from Amazon.
One, Silicone Power 128 gb SSD: ~$17 from Amazon.
I used a keyboard and monitor I had to get it set up, but now it's freestanding.
I don't know how many VLANs you're talking about, but I run a LAN for security and the OPT interface is for multiple Static IPs from Google Fiber. I have it attached to a Netgear Gigabit 8-port switch I got off Amazon for ~$19
The built-in NIC on the HP Prodesk provides the WAN. I get full speed 1 GBs through the Fiber Jack.
So, outside of my time I spent a total of about ~$125 and it seems to work just fine.