There are no set-in-stone rules, and the question is to vague. Too many variables.
Obviously it depends on the content. One page of powerful information, something that helps people make money or change their lives for example, could be worth $100. A 100 page rehashed junk ebook could be worth less than a buck.
It also depends on who you are selling to. Like kindle you might have to stay in the $2-$3 range. It's just the selling mentality there. Selling to professionals could fetch higher prices.
Just as important (if not more) is the title of the ebook, and the sales copy. Best book in the world won't sell much if the title and sales copy stinks. Gotta make them want it real bad.
Plus, if your reselling some one else's ebook, you will probably have to go with a lower price because it's likely you won't be the only one selling it. Not mention you have to compete with marketers who think it's a good business strategy to sell stuff for next to nothing.
Obviously the content needs to be good. Verified by others besides the author. Authors, especially those who are not writers get to close to it, or don't see the mistakes. Have some one else proof read it. Something I don't do enough of.
As a rule of thumb, if your selling it on your own, like your own website, you can go from $7 on up. $17 to $37 seems to be the tops unless it's really good or comes with lots of extras. But again, it depends on the content and how well you can sell it. 7 is a magic number but I can't remember why right this moment.
If your selling your ebook with resale rights or plr right, that can and should get you a higher price. Adding bonus items like checklists, mind maps or resource guide can help sell and get you a higher price as well.
Just my opinions. And selling ebooks for quite a few years.
