Update: Sold out, but the similar NETGEAR Orbi mesh system is also on sale for $350 right now. Or you could install Fedora on a spare laptop with an extra USB network card to use as a router and firewall, and find some extra routers at the thrift store to act as repeaters.
Eero basically invented the mesh router market, and their new wireless system is a marked improvement from the already impressive original.
Amazon’s currently offering the Eero 3-pack (one base station and two beacons) for $300. That’s a big chunk of change, but it’s $100 less than MSRP, and easily an all-time low price. The Eero base station is basically a small but powerful Wi-Fi router, while the beacons plug straight into the wall and work with the router to create a strong mesh Wi-Fi signal throughout your entire house. They also double as night lights, if you weren’t already sold on them.