I'm not sure about the cost effectiveness
but the way we've done our feeder breeding has worked out well
we have our mice colonies set up as: 1.5 mice (we have 4 of these)
and the rats are: 1.4 rats (we have 2 of these)
but we use rather large enclosures compared to
we've got 4 of the mice colonies going without a hitch
our rats breed, but it seems to be on their terms, not on ours, they just dont breed as efficiently as our mice do