I'm not going to give my 27 year old son ANOTHER $1500 so he can attend my wedding in the Bahamas
Does he go through a lot of money? Is he still living at home?
He's not living at my house but he spends a lot of my money.
I understand how you feel, but it is good to take care of your kids. Plus if you are having a wedding in a foreign country you can't expect other people to be able to travel there.
So I not only have to pay for the wedding but for his travel expenses too?
Weddings are very expensive, especially a destination wedding. Since this is your wedding you'll be expected to foot the bill. You could possibly ask your fiance to help if the cost is a problem for you.