The cost, of course, will be determined by your needs. Do you want multiple zones? My desire was to have all the common areas driven by the same source. So I only use one stereo reciever and a speaker switch (it can handle up to 4 speaker sets). And then a single Express connects to the reciever. This is the simplest and least expensive set up in my opinion.
Typically the more zones you want the more expensive the set up can get.