We were married in Maui 5 months ago. I planned it all myself and it was very affordable (as far as weddings go). It was on the border of Kihei + Wailea. The ceremony was on an oceanfront lawn and we did beach photos after the ceremony.
I picked Maui over St. John because a) we're on the west coast and it's an easier trip for most of the people who attended, b) Maui has a lot more to do overall for the guests for the week they have, I think of St. John as being quieter (tho I adore St. John)
We had 13 guests. I rented 7 condos (oceanfront). The lawn in front of the condos was beautiful and quiet and FREE (because we were guests). Everyone loved their condo + view.
Email me if you would like to see wedding photos to give you an idea of the location.
Although it seemed a simple idea, it still was very stressful because a) you worry that everyone who is coming and spending their money is going to have a great time, and b) we couldn't spend enough time with everyone.
Good luck!