How many is multiple rooms?
So 400x rooms is the budget. What is the total.
Is this background or more critical listening.
Speakers go from $60 a pair up.
Do you want to be able to stream the same source to multiple rooms? Your current plan would not really allow this.
Sonos is a good plan but your budget is tight for multi room.
500 for source like Sonia and 100 per pair of speakers so 600 a room gets what works really well. Either Sonos. Control4 or something with more room room grow.