We are booked for a St. Lucia to Grenada charter next February. We found that if we stayed somewhat flexible and did some searching we were able to find pretty good deals on airfare. We actually ended up on American both ways and though we could have flown home cheaper on JetBlue, the itinerary didn't work as well for us as American did. In any case, I don't think it cost us any more for that itinerary than a round trip from a single destination would have cost. I find that round trip tickets these days typically cost about the same as buying two separate one-way tickets, and sometimes if you switch airlines you can often save money over a round trip on a single airline.