Sonos is expensive because of its wireless system, not because of its lackluster sound quality. It uses wifi and each speaker has a wifi network interface inside of it. Not sure if you are forced to use the sonos base system or if it can utilise your home router.
There is no home brew version of it. From sono it falls down to receivers and then utilizing some wireless speaker tech (usualy each tech handles 2 speakers/channels at a time).
Wireless speaker tech is still in fledgling stages due to no ready made standards for wireless audio short of bluetooth standards. This usualy means new tech that needs to be created has to tackle issues like signal degradation, interference, and latency.