I'd like to get all the Jack Reacher books for my Kindle app, but that wont happen any time soon due to the price of them.
I did recently get the entire Quiller series, after I found that I only had less than half of the paperback books, and never knew the others existed. They were mostly in the $6 range ($A), which was ok for a Trad, with 1 exception which was in the $13 range, but I paid it anyway. Obviously OCR'd without an edit afterwards, but still better for me these days than the paperbacks.
I increased my prices from 2.99 to 3.99 at 3 years in, then to 4.99 at 4 years in. Leaving book 1 at 2.99 as the taster.
When I got to series 5, I figured book 1 was no longer the main entrance point for people, and put it up to $4.99 as well. It continued selling just as well, and made me wonder how much money I'd been leaving on the table for how long?
I did mention price increases to fans at one point, and they were fine with it, although several said they'd rethink if the prices went over $5US.
That seems to be the main barrier, and I've no plans for going over it at this point.