I got my copy of Dreadnought through Advanced Book Exchange:
www.abebooks.com
They have several copies, the lowest shown being $25.41
http://dogbert.abebooks.com/servlet/...eadnought&x=18
I would also recommend David Lyon's The First Destroyers; but only if you are interested in 1890s Torpedo Boat Destroyers.
http://dogbert.abebooks.com/servlet/...estroyers&x=24
I'm surprised at how cheap this one is-I paid $25 for a new copy a year ago.