And since it takes at least a nuc (mini or otherwise) to raise a queen, most breeders in the north are "micro-breeders". They perhaps raise 25-100 queens at a time. Mainly because it takes some real effort and resources to set up and get going large amounts of nucs every spring.
Down south, mini or what they call "baby" nucs are sometimes used, especially by the bigger operations. Some baby nucs use as little as three combs of about an area of 5x5 inches each. Not really conducive to allowing the breeder to evaluate the performance of a queen. But it takes little resources to keep them going all season.
For those beekeepers reading this, especially from the northern areas, some good information can be found here: http://www.nsqba.org/
We need more local queen producers all across this country.