Sailboat Harbor Cruises for my Proposal?

Hi y’all. I am hoping to propose to my girlfriend during our trip to Charleston. My idea was to do a private sailboat cruise either in the morning or evening. Most of the ones I have seen are about $500 for the 2.5 hours which is totally reasonable but I make a teacher salary so If I can find a cheaper option and/or find someone on craigslist with a boat to sail us around, I will definitely prefer that. Anybody have any suggestions on companies to look into or advice?