Ubiquiti ERLite runs Vyatta on Debian on MIPS. $100 and it has TCP + VPN offload and 3 real interfaces. It might be possible to run PFSense on it; I've installed PFSense to a CF card on an IDE adapter running in a thin client (you can also find these on eBay, some with PCI-E even...check out the HP T5745 for example). You can find a lot of thin clients on eBay for under $100 if that's what you want, and most are fanless and low-power. The only issue is fitting multiple NICs, but again, PCI-E if you know where to look.
I offer them on ebay for $44 + Shipping. It is not hard to just build your own. 3ghz core 2 duo machines with 4GB and room for a 2nd NIC are the way to go to keep cost down in my opinion.
I only entered the market by accident. There is not much of a barrier to entry. I bought 50 machines from a recycling company in Maryland for another project. My friend suggested putting pfsense on them and selling them on ebay to help get rid of them. Your lowest cost product is $299. I am sure you know this industry better than I do. Ping me offline if needed.
No, we only sell ~4 machines per week. Profit margin at this price is thin. Maybe we need a better marketing campaign :) The machines without hard drives cost me $20 each. I got a bulk deal on hard drives and network cards. Once we sell all 50 machines, we don't plan on selling any more.
So, why isn't selling cheap pfsense devices on eBay part of the solution to avoiding vendor spying? Because you also sell pfSense hardware and it's more expensive?
I wonder what's the cheapest/most low-power hardware that could do that job? A Raspberry Pi is too underpowered (putting Ethernet on USB is also a big problem), but what's the next step up from there?
1.8GHz dual core celeron, 2GB RAM, 25GB SSD, wireless + gigabit LAN, fanless and in a nice box with power supply for $100 + shipping.
Disclaimer: No idea how difficult it is to purchase from taobao internationally and this vendor/model may not be the exact one I'm using, but it gives you an idea of the economics that are possible.