Thanks for the info Mich! My travel agent also had a contact at Epic Travel who gave a very similar quote to Brown's (Epic was a 47 person tour bus for $600), so I feel pretty comfortable.
JGAMMAGIRL77 - I also considered not providing transportation and I think that it totally depends on your guests. I know that a lot of my good friends would have just been excited to have the cruise taken care of, but I thought that some of our family and older guests would expect the whole thing to be planned for them. (Plus, my worry with everyone getting there on their own was that some of them might miss the boat since it is a public tour... just something to think about if you have people that are not very punctual).