Comment by zrm

You can get copper ones for $5.99 (quality may vary):

https://www.amazon.com/1000Mbps-Network-Performance-Gigabit-...

https://www.amazon.com/SALAN-Ethernet-Portable-Internet-Conv...

But it's not competing with those, it's competing with the copper port which is already built into most devices.

Another thing that would work is something like this (also $5.99), but with one of the ports as fibre:

https://www.amazon.com/Gigabit-Ethernet-Splitter-1000Mbps-In...

The point being you need some cheap way to plug in existing copper devices if you run fibre to the endpoints.

This plus $5 for a transceiver is pretty close at $15:

https://www.amazon.com/Gigabit-Ethernet-Converter-Auto-Negot...

But +$15 and an extra wall outlet per endpoint is still an inconvenience, and if a two-port device with its own power supply can be made for $15 then where is the PCIe/USB to fibre adapter for <$10?