I would avoid integrating Sonos with any control system if at all possible. Their last update broke integration with Savant and most likely others. Sonos on its own for audio is fine.

What streaming services do they use? Autonomics with your flavor of amps would be a solid solution using as many streamers as they need. We lean towards single zone streamers so they can have as many unique accounts as they need, 5 different Spotify accounts for example.

As for budget its hard to sympathize with someone that has 30 zones of audio they are out of money. Don't let the budget dictate you into a less than optimal system as you will pay for this for years to come. Give him 20 zones of audio and add the last 10 when they come up with more cash. ;)