All I need is basic stereo (2 channel) output.

Basic Requirements:

3 sources
4 zones
15 Watts/Channel

The essential functionality I am seeking is independent
source selection & independent volume control in four rooms
(each room has a pair of speakers mounted in the ceiling.

Source selection and volume control could be made
from either fixed (e.g., wired to wall plates)
or by handheld (i.e., wireless) remote controls.

I have seen mention of the following manufacturers
as producers of "Multi-Source/Multi-Zone" audio
systems but I suspect that most of them are sold
through "exclusive" dealerships ($$$) rather than
by the more competitive mass retailers.

Channel Vision
ChannelPlus
Denon
ELAN Home Systems
Marantz
Niles Audio
NuVo
Russound
Yamaha

Do you know which of these vendors has the best
pricing for a system that meets my requirements?

Are there any "mass makers" of such a system?

In any case, do you have advice on how I can find
such a system at the lowest possible cost?

Thanks in advance!

Errol