This is highly-dependent on the system design, as you can have all sorts of combinations (local vs bus power, length/quality of cable, EMC/EMI considerations, whether the slave is a mic node or requiring I2S/TDM and all associated external components, etc.). The transceivers themselves are $2-5, and the lower-cost AD2429 master (and possibly the AD2420 slave counterpart) might be candidates for such a single master/slave topology.
