Hello Avril and All,
Two of the general books I use are: The Audubon Society Field Guide to North
American Seashells and A Guide to Field Identification Seashells of North
America by Abbott/Sandstrom.  I don't know the price of the books, but they
are not expensive.  More expensive books would be by Dance, Lindner (an
excellent book if it could be found), Holt field guide, and others.  The
first two I mentioned are only for N.America.
    A good starter collection would be one or two representees from each
family, showie or "pretty" shells.  Here on Long Island I bought a bag of
shells from an import store that imported objects from the Philippines.  That
is where I bought my 4.5 foot Tridancna gigas, was outside now sold to a L.I.
Shell Club member who put it in the living room!
Jordan *