That's a good price. And yes they breed like crazy. Fatten them up on higher protein foods before breeding, and you will get larger spawnings. At this size, they probably have already been breeding last season. So just feed em well, keep the water clean and ease up the temp. Mine spawn at about 77-78 on the low side.
I think hours of light have something to do with it too, but haven't found a way to test this out yet.