This is more of an accounting function than networking, and ideally not limit by MAC but signon, but OK u don't have one of those fancy MS Domain setup.
I frequent pfsense, and sounds like u can do it there. Pfsense software is free and you can run it on an old PC with 2 NICs, but as already mentioned, configuration not for street-Joe newbie.
Recently I have come across some boxes at amazon, they don't call them router or firewall but have very home-friendly names, and seem to be marketed for the home user who needs more control over usage/users (kids?), and priced to match (not cheap). Don't remember what they call them 🙁