I'm looking for something along the lines of this;

If you don't know what they do, you hook up one to the wall near your router and hook up an ethernet cable between the two, and then one next to the far-off computer and hook that from the wall to the computer.
Problem is, those cost $50 bucks each. Used! I'm not about to shell out 100 bucks on those.
Any other ways I could go about this?