Jeff, there is no such thing as a mini Cocker Spaniel. The breed has a standard that states that boys should be between 14.5"-15.5" and girls should be 13.5"-14.5" tall. The ideal weight is typically around 23 pounds, although it varies by body type.
There are certainly smaller Cockers out there, but breeders marketing "mini Cocker Spaniels" are probably just out to make a quick buck.
Does anyone have some information on mini Cockers? There is limited information online and not that many breeders.