Earlier quoted context omitted.
> The problem to be solved is that you want to be able to put fibre inside the walls of the building instead of copper. Running a new cable to the switch closet is the thing to be prevented. ...why would you ever not run copper alongside fiber for new construction? If nothing else, PoE is extremely useful, and nothing says that you actually have to connect all of that copper cable to your switch... you can connect it…
The original problem was that everyone runs copper instead of fibre because there are too many existing devices that only have copper. Running both everywhere would require you to buy and terminate twice as much cable as you expect to use, which leads people to running only copper again. If you chose PCs to begin with that come with fibre ethernet or put quality cards in the ones that matter then you could make fibre…
Ah. Let's play with that logic a bit:
"Running Ethernet cabling everywhere would require you to buy and terminate far more than twice as much cable as you expect to use. Just run power cables and wire up one extra outlet for a HomePlug in each room.".
Yeah, that checks out. "Powerline Ethernet" devices are actually pretty good these days, and are right around your magic price range... Amazon has them at ~13 USD per unit. [0] Why would anyone bother running a second cable to each room? Thirteen bucks per room has to be way less than the materials and labor cost for the cable run. Doing anything else is, like, really stupid. Don't you agree?
Anyway. You expect to use the cabling that you plan to install... plus some extra for screwups, man.
[0] https://www.amazon.com/Linksys-PLEK500-Homeplug-AV2-Powerlin...>