How do you manage to get the books the at the kindle sale price when you don't own a kindle? Strange, when I got my Nexus 7, I did give the kindle app a try but

How do you manage to get the books the at the kindle sale price when you don't own a kindle? Strange, when I got my Nexus 7, I did give the kindle app a try but it wouldn't let me purchase any books unless I paid the hardcover price. I have amazon prime, but without owning a kindle device, these ebook sales are meaningless to me.