You could always buy another Echo Plus, they're relatively cheap, good bass.
Sonos is excellent, but in a different way than your stated goal. It has the streaming client software built into it, so it plays the music, you don't stream to it, but you can stream Spotify Connect from Spotify app on your phone, or use the built in Spotify app inside the Sonos. It will play every streaming music service, every online radio station, any music hosted on your own LAN, and it will sync to other Sonos elsewhere in the house. And it has programmable alarms to play your favs automatically on schedule. It's a pretty nice system. But no bluetooth on the $200 speaker model. https://www.amazon.com/dp/B07W8ZVXWR/
with or without Alexa
My son lends me his DOSS bluetooth speaker
when we go away for weekend. Works good for $30.
BOSE and JBL also have very good bluetooth speakers in your price range.