Just for fun, I went to my local Staples website. The main 4-line phone with answering machine is $189 and the other phones are $139 and you still end up with crap and have to wire a pair if RJ-14 jacks at each location. That and the fact you can't use a single line set across all lines ought to be a deal breaker in anyone's system.

Oh, RCA has a goofy cordless that's mated to a single PHONE.
It ain't cheap.

Carl