I suggest you contact my mate Ed at
Famhard@aol.com
He's a dealer on the west coast for Whites detectors (and others I think) and can (and will) happily advise you on the best detector for the beaches. I suspect he'll tell you to get a Whites DFX. You can also get decent used machines, and yes, they do come apart and will fit in a suitcase. Not sure about carry on though, you'd probably get stick from the securiity folks.
I know that when (some day) I manage to get to Aruba, I will be bringing my machine. In the meantime, I have to settle for the finds I get here in the UK.
Hope to meet you all (eventually) on the beach there.
Cheers,
Greg