It varies wildly. My main setup are DIY-built "Amiga" speakers, on a Yaqin tube amp. I also have Overnight Sensations speakers in another room. Definitely go DIY if you're looking at something new.
The cheapest is a recent $10 portable bluetooth speaker (via aux in) for the shower. It turns on when the shower door closes.
I guess this comment is going to be a defining example of a useless HN comment, but I've been sitting here aghast and trying to express what I feel about this.
Ha! I mean, it's an $8 contact sensor, and a $10 speaker, and the Raspberry Pi I used for snapclient was already nearby and could handle it. (It was/is doing network monitoring).
I did it because, well, I wanted music in the shower. And it is nice getting the house text-to-speech messages in there too.
(Also it changes the lights in the bathroom)
Home automation is pretty fun once you hit a critical mass of sensor data. You can usually implement new features with a single additional smart outlet or contact sensor. For instance: For awhile, I had a neighborhood cat coming by and marking my patio at night (my cats, who I let out during the day, immediately ran to smell it every morning, and I could verify that was indeed the problem with my security cameras).
I bought a powered, default-closed solonoid valve for my outdoor faucet. I already had everything else--a sprinkler/hose, an unused smart outlet, motion events from my patio cameras, I knew if my doors were closed, etc.
So I added automation to: If patio motion at night, and my doors are closed (so my cats aren't outside), and the bedroom is in night mode (extra check so I don't accidentally hit my cats), and it's above 45F outside (don't want to freeze a poor thing), and there's motion on my patio, turn on the sprinkler for 15 seconds. The outdoor cat got caught once, then learned to fear the click of the outlet engaging but would dodge in time, and then never came back.
