Help! Miami, FL "quick" Wedding - Airport?

I am writing on behalf of my niece who has asked for my help with her wedding. We are scheduled to go on a cruise in February, 2007. My niece and her fiance` would like to get married on the ship; another niece did this five years ago and it was wonderful. The problem with this is that Carnival has now jumped the price to ridiculous amounts. My sister and brother-in-law cannot afford to pay for this on-board wedding and ALSO go on the cruise; there are about 12 of us going on this cruise. My niece wants to get married and be able to wear her wedding dress - I understand this completely. My friend and I were trying to come up with ideas to get my niece and her fiance married (perhaps in the airport?) and then go board the ship - in her wedding dress and all her glory. Help! Ideas please? Thanks! Robin