Many snakes do need their temperatures to change around the year to mate. I don't know of any book that focuses specifically on breeding kings, (though I'm sure they're out there) but there's the book, "Kingsnakes and Milksnakes A Complete Pet Owner's Manual" by Markel and Barlett and published by BARRONS (I know it has a few pages on breeding) and I'm also fond of the AVS or "Advanced Vivarium Series" books which have always struck me as being quite informative. If you ask in the kingsnake forum, I'm sure they can give you some good titles. There's also a webside called www.anapsid.org which has tons of articles. Might be worth a look.
Ten hatchlings at $40 does sound like a lot (and some clutches have more), but there are some things to consider which will chew away your profit something nasty. Both the male and female king will have to be housed separately since the species is known for cannibalism. That means 2 seperate cages, 2 separate heating elements and controls for elements, the electricity for both snakes year round, food for both snakes year round, incubator for eggs (I've heard people can often make good homemade ones with the right instructions) separate secure containers with heating elements for all the little baby snakes since siblings will eat siblings, food for all the little baby snakes (and here's hoping they eat willingly).
Then I've seen baby MBK's for sale for $50 and a very handsome adult for $80, but if you sell to a store, they'll probably only offer wholesale or $25 of that fifty. You could advertise and sell on your own to take full price, but that would probably involve a fair amount of legwork.
I'm sorry if it seems like I'm discouraging you. Breeding snakes is an awesome endeavor and a great challenge to take on. (kinda like climbing a mountain because it's there)
It brings new information to the hobby, captive breeding lessens the pressures on and protects wild population, and I've never bred snakes myself, (I will someday) but it's gotta be an awesome experience for the breeder and I can imagine the thrill of seeing those little heads poke out of their leathery shell the first time in their little lives. But frankly, breeding for money's a whole other ballgame and you'd be doing very well by just breaking even.
Good luck, whatever you decide. 
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0.1 chickens (Condor)
0.2 dog mutts (half ownership, only mine when they misbehave, Lucy & Amy)
0.1 Halflinger horse (Crissy)
0.1 Normal phase California Kingsnake (Sophia)
1.1 parents
Still searching for 1.0 WC human