Is "cheapest" the right objective? Because if that's the case, book piracy seems like the clear winner. But maybe we should consider "cheapest with some boundaries". For instance, we probably agree that bookstores are nice for a myriad of reasons, even if we don't frequent them. They employ people in the area, they offer curation and recommendations, they invite speakers and host events, and they help local authors g…
If I want to discover a book I don’t know about, curation provides value. If I want to attend an event, some place holding an event provides value. If, on the other hand, I know what book I want, the curation is done and I’m not looking for an event, so cheapest seems a reasonable thing to optimize for.
Until you find out that the cheapest source also waits two weeks to send your book. And sends it by a method that takes another four weeks. And doesn't package it properly so it arrives with the spine broken and water damage. And sends you a used book with pages missing. Or might just accidentally send you the wrong book but doesn't have a customer service contact.
The internet used to be a great place for bargains. Now "cheapest" is almost always the wrong choice.