One thing to consider: If you CAN bring the goods down as oversized luggage, there is a 'slight' chance you can walk them through customs w/ out paying duty on them (depending on the whims of the person you deal with, if you can convince them the items are for personal use/that you are taking them back OUT of the country when you leave, etc.) If you ship them down, you WILL pay duty, possibly at the assessed value (as opposed to declared value, again, depending on who you deal with and what kind of mood they are in that day.) You will also pay sales tax... I'd call Hyde (Nelson or Benny) and get a quote and then decide. You WILL need to ship the goods to Hyde in Medley. You'll also need to figure out how best to get them from Belize City/port to San Pedro (that is, if San Pedro is where you are heading.) Tropic will fly them on a space-available basis... cheaper option might be to put them on the Thunderbolt (//www.ambergriscaye.com/thunderbolt) They can carry freight and have boats going several times a day.
As far as I know Hyde does not let passengers on their vessels. Neither does Amerijet (www.amerijet.com) who has cargo flights from Miami to BZE every week...