If you happen to have existing coax cable runs in your house, you might look into MOCA. It's used by some modern cable tv boxes and similar devices to route eth

If you happen to have existing coax cable runs in your house, you might look into MOCA. It's used by some modern cable tv boxes and similar devices to route ethernet packets over the existing coax cable. It can be used on the same coax as is used for your cable modem, though if you can isolate the coax you want to use as an ethernet link, you might have better results. I've used the competing standard DECA in the past, as it was significantly cheaper than MOCA about 5-8yrs ago ($25/unit vs $150/unit) but MOCA is now the much better option with it supporting GB speeds and pricing being down around ~$50/unit. I think the max speeds I saw over DECA was about 100Mbps, maybe 200Mbps on shorter runs.