[Sporadic]

Originally Posted by Daithi

I'm not sure if these qualify, but Laura Lippman (a mainstream author) has several short stories available for $0.99 each

The Babysitter's Code
Hardly Knew Her
A Good Fuck Spoiled
Dear Penthouse Forum (A First Draft)

I don't know if I should add those since a single book of all of those short stories are avaliable for $6.39

Joe Hill (Stephen King's son) has the same situation. You can either buy his book of short stories for $8.39 or you can buy the short stories individually for $0.99 each.