Oh boy, Oceanfanatic, does this scenario sound familiar. It's my inlaws who are tight with a buck and don't have to be and my parents who are doing ok but like to live it up a bit! When DH and I got married it was always "how much did you pay for that" and this and that. The planning of our wedding made them mad (they thought it was too extravagant, it was actually average) but hey, they didn't pay for it. They reuse paper towel and dixie cups and they wash the plastic forks and use them over and over again. They brag about the $4.95 Fish Fry they ate but don't talk about whether or not it was any good. When we took both sets of parents on the Glory this past April, everyone got along just fine considering the differences. Of course, DH and I paid for the airfare, hotel, transportation, and the cruise. My mom in law brought along US stamps and bragged about mailing post cards out of ST Thomas for much cheaper with her own US stamps. My mom said she bought regional stamps because they looked neat and even though they cost 3 x as much that was ok. My mom in law thought my mom was nuts but.... Differences of philosophy about money for sure. DH's parents raised 5 kids on one income so I cannot fault them for the way they scrimped and saved money. But DH and I and the rest of the world are kind of inferior in their eyes because of how we handle our money.
That said...here is what I have had to politely say to my inlaws -- It's our money, we've have earned it, we are financially stable, and how we spend our money is private ...etc... For you I would simply state that we are on vacation and want to have a good time. We have planned for this trip and budgeted money and we want to enjoy ourselves and not worry about how much it all costs. Therefore, we are taking the direct flight, booking private transfers, staying in South Beach in our own room and booking the tours we want to regardless of the price. If you want to join us, great! If you would rather do something else, feel free.
I know some of your plans are already made. But please don't allow these folks to dictate how you spend the rest of your vacation because they want to force upon you their values about money. Taking a cruise is a vacation you want to go on and have a blast, not have regrets about what you wanted to do but didn't.