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.