I suspect it has to do with feeder costs for the low end. I haven't bred boas but I'm going to guess they cost more to feed as babies and $40 is the bottom line that a baby can be sold for in order to recup the higher food costs. Ball pythons are cheaper to feed so the normal morph can be sold for less.

Regarding higher prices, I think Aaron was dead on with supply and demand. There is a greater demand for ball python morphs so they have a higher value. Of course supply and demand play into the normals too but there is a very strong market disincentive to sell for less than your cost so I suspect feeders' costs set that bar.