If first books were universally priced at 99¢, the only folks who’d lose are authors who won’t write or can’t sell a second book. I say, let’s set that expectation!
99¢ is a good price for a single “taster” book so folks can be sure if they like your books. If so, they’ll pay full boat for the others. If not, you don’t have a frustrated reader who feels ripped off, you just have someone who quietly goes away. Folks who pay $12 for a book they hated are far more vocal than folks who only paid 99¢.
Be clear with your readers that’s exactly what you’re doing. “This book is the taster sample. If you like it, here are 6 more!”
Everyone in traditional publishing mourns the loss of the gatekeepers. This is built-in thresholding. Don’t set the bar artificially from the outside, set the bar at “Do you want to write a book badly enough that you’re willing to sell it for 99¢ because you know you’ll be writing more?”