Could be propagation difficulties. That's partly why some rare grafted or budded trees cost over a hundred dollars in a small size. Or maybe demand is low, so fewer units are produced, making production cost higher than for something that comes out of a plant factory. $20-$30 for a one gallon specimen of a choice tree or shrub is not that bad, as far as it goes. However, with fall clearances on the horizon (if you have those down there) maybe you will be able to find one at a discount somewhere soon.