I periodically check up on Amazon’s monthly deals. Though the science section is usually pretty thin, the history deals are more numerous. A lot of them are not too good, or are reprints of very old books. But now and then you get a scholarly and dense work which is magically priced at below $2.00.
So I bought a copy of The Roman Empire and the Indian Ocean: Rome’s Dealings with the Ancient Kingdoms of India, Africa and Arabia, and skimming over it it’s definitely not the most scintillating prose, but there’s a lot of interesting material in the book. If you are looking for a good book, I would recommend it, especially at that price.