hi there,
I'm not experienced, but i do know there's demand. I know nothing of corns, only royals.
Primarily, if you want to make extra, you have to spend a little extra and get some good quality looking snakes. this also depends on a morph you decide to take on.. AND this also depends on how many, like someone has already said.. feeding costs can mount up.. i've 25 snakes at the moment.. my feeding bills are high ~ £70/month roughly. Once these grow older, providing they all eat.. the cost will also rise (along with what i produce). the most profit is made from simple recessive snakes, because they hold their value. Luckily i can afford to keep them, so the mounting costs doesn't bother me.. i love them regardless... and i will continue to.. i'll never sell them!
you mentioned royals...
i'd say pastels, they are still fairly cheap and can produce super's, which can also lead onto better things, but they are also beginning to get quite common.. this lowers the value fast as they are also co-dominant. There are other co-dom's, that i'd say provide value due to the supers they produce.. mojave, lesser platty, pastel - super pastel and more... But, then you can get value snakes where they produce amazing combinations.
to be honest dude.. if you want in it for the long haul.. get into double hets, this means buy different morphs.