Are you in the US? Arylic A30+ are on sale for $97 (which is wild because they’re $219 CAD on .ca). Four of these and you get complete zoning and the ability to link them together through their app, so everything can play the same thing or something different. AirPlay, Spotify Connect, USB, and analog audio in… They’re solid little boxes. And for under $400, four stereo zones of amplified audio is a steal.
You could get away with purchasing just two A30+ and wire two speakers per channel (two zones per A30+), which assuming they are 8-ohm speakers, would result in a 4-ohm load which the A30+ is good for 50-watts/ channel at.
Edit: If you pop the grill off the in-ceiling speaker, it should show a model which would allow you to verify the speakers impedance to ensure their 8-ohm, but 4-ohm in-ceilings are kind of rare and I’m doubtful this is a 70/100v system.
Denon DN-350UI or Tascam CD-400U with IF-E100 expansion card. Denon would be more in your price range though and has a lot more options.