It looks like the game may have gone on sale from some of these sellers weeks ago but it's hard to tell because it's not a high-profile game to begin with and like with other Osprey games it is listed as a book and not a game. All other online game retailers have the game for $32-40 before shipping. The last time I found a deal posted for this game was a July sale at $24.99 from CoolStuffInc.
I don't know anything about this game but I noticed it while browsing the Osprey listings. The one text review makes it sound fun if you're really, really into submarines shooting each other. I'm not. I like my submarines to make love, not war.