Yup. Before wifi was widespread and standard on computers, this is how ALL computers in the house connected to the ISP.
You had them running all over th e house and they got installed similar to phone lines (before everyone had a cell phone)
And Ether net cables are not that expensive. If you look on the back of your router there should be a place for a connection which looks exactly like a larger version of the old landlines phone connectors and connects the same way just by pressing down on one side of it.
You can see it in the photo at the link. Looks just like the phone line connectors except larger.