Cheap? How about using AirPlay? iTunes has had it for a while, lets you play out to any or all "zones" that have an airplay destination device such as many AVRs, Apple TVs, or AirportXpress units. The lowest cost solution is probably using AirportXpress units for each zone and a low cost amp for that zone. Beats Sonos if you're careful, and offers play control, individual volume controls, and zone selection via iTunes and via iDevices using Apple's Remote app. The limitation is it's all a single stream from a single iTunes library. You can have multiple iTunes libraries running simultaneously, but each has to be on it's own computer. You can also stream Pandora that way, and perhaps others. For multiple sources you'll need something other than a simple amp per zone, and that gets you to a low cost AVR with AirPlay. Now you can have multiple sources per zone. Remote it all with your favorite iPad-based remote control system, and you'll have exactly your goal.