My friend also got married in Jamaica. She had a pre-wedding party about a month before the wedding. It wasn't really an engagement party, but more for friends and family that couldn't afford the $1,000 ticket to the Jamaica wedding. If your guests are paying their way to attend the actual wedding, then I don't think it's right to also make them pay to attend your engagement party. If the main reason for having this party is just to inform your guests of vital trip information, then I'm sure they would much more appreciate a simple, printed out sheet of this information tucked in with the invites ~ rather than having to pay even more to simply get information that you should be providing anyways.