Female co-doms are worth more because most people buy a male co-dom, breed it to normal females ... dump the males they produce as fast as they can and try and hold on to as many females as they can afford to keep in order to make supers (homozygous) and crosses with their other co-dom males. More males available = more supply = lower price ... less females available = less supply = higher price ... supply and demand ... basic economics ... no mystery there.
-adam