WarGameVault is basically a site catering to historically-based gaming.
Among their daily special offerings are sometimes books that are very much non-fictional (I suppose they're there to help gamers make things as authentic as possible?). Today's special of the day is one of them.
It is Warfare on the Mediterranean in the Age of Sail: A History, 1571-1866. It's authored by David S.T. Blackmore. It's 402 pages long.
I could dig up only 3 ratings. That's not nearly enough to meet my criteria (20 or more). But, the ratings are all "5's." Furthermore, I made up the rule, so I can break it, right?
Oh yeah, the price. It's only $4.50. The Kindle is $14.74 right now. The only annoying thing about WarGameVault's books is that they are "watermarked PDF's." I have not bought a book from WarGameVault yet, so I don't know how obtrusive the watermarks are.
The deal is good for over 17 hours from now.
More
here.
It's a must-buy for me. I've gotten very interested in this subject since reading a biography of Ferdinand Magellan recently.