There are a lot of variables. Pier and beam or slab? It can often be easy to run wires under the house in pier and beam, not really an option for slab. Single story? It is usually pretty easy to run wires in the attic, but dropping down from the second to first story could be tricky without opening up a wall.

I paid a cabling company to wire up my old house. Cost a few grand and they figured out the path (attic, crawlspace, and in some cases the exterior of the house). I have a UniFi system so I got PoE WiFi access points and PoE 4K cameras installed at the same time.