I don't have time to read mediocre books. I've found myself buying a number of ebooks and putting them aside, at several price points. I think I am more wary of the sub $9 ebooks, which may not make sense, but there you are.
All these books under $5 are, from my point of view, priced so you take a chance on something you don't know. Not for me. However, if a book I know I will use (and therefore worth North of $20) happens to be priced at $5, then so much the better.