So, my setup is my personal project that my wife has no interest in. This is important because it all comes out of my discretionary fund which never gets too big, so I had to build it in pieces and for cheap.
The first thing I got were new speakers for my PC. This left me with some Logitech 2.1's that connected through a 1/8in jack. Next I got a Chromecast Audio, plugged it into the 2.1's and set that up in the kitchen. I downloaded the home app, hooked up my google music account, and now could say "ok google, play music in the kitchen". Worked great, cost under $100.
Next, I told everyone that loves me that chrome cast audio's and 2.1's are always on my gift list. So the holiday's roll around and I get two more audios and one more set of speakers. I went out and got some bookshelf speakers and a smaller amp from amazon. Those became the setup for my living room and dining room.
Using the home app, I named all the Audio's based on the room they were in then grouped them together as "downstairs". I cracked and bought a Google Home (though now you can make one from a raspberry pi and they're talking about the next generation being a router as well).
I also have two Google Videos named properly, so now you can say "play music on [location]" to get tunes anywhere downstairs, or 'play video on [device]" to get shows on the projector downstairs or tv upstairs. And, since it's all chromecast, you can of course do all of these things from any android phone on the network (we keep it open for parties, but no one ever really uses it).
I also have a nest thermostat and protect, and some switches coming, but those are more for energy efficiency.