I noticed that there is a copy of Frank Fox's first book, Great Ships: the Battlefleet of King Charles II, for sale at Albion Books. What is significant about this book is the priced. I own multiple copies, and never paid more then $80 (US). This copy is for sale at $254.53 (converted to dollars from pound sterling, presumably).
I would expect that unless someone is really wanting this book and willing to pay a premium, this copy could be for sale for some time. I use Addall.com/used for finding used and out-of-print books. I have consistently found that more useful than Amazon, although for finding Frank Fox's second book, A Distant Storm: the four days battle of 1666, the only option seems to be Amazon.co.uk.