What company are you going through for your catamaran? I've seen some mention of vendors on here that will do 2 hours for $900 for up to 40 people and it includes appetizers and open bar or something like that. That still may be out of my price range but I thought I'd still look into it.
I thought the s'mores party would be a nice casual idea for the welcome cocktail the evening everyone gets there or the day after so everyone can mingle. I'm expecting 20-30 people so that doesn't seem too bad.