I don't know how much a typical flight to st. lucia is, but for us, we would have flown to mexico, then to st. lucia, then home. So, it was going to be about 1000 pp, for our flights, which isn't bad for all those flights, but we're only going to spend about 350 pp on flights to mexico, so we'll be saving 1300 dollars that we can put towards our honeymoon.
When I was looking at Antigua the flights were expensive, I think a lot of the smaller carribean islands are more expensive to fly into.
But if you don't have a TA yet, you may want to contact tammy (host) and she can probably give you some advice, she is a TA and specializes in destination weddings, she'd be able to better answer this question than I can.