My list of transfer services based in Corozal...
a) Belize VIP Transfer Service, http://www.belizetransfers.com
b) George & Esther Moralez Travel Service,http://www.gettransfers.com
c) Gibson’s Tours and Transfers,http://www.gibsonstoursandtransfers.com/index.html
I know a family who used a transfer service to bring their cat with them to Belize. I can't remember which service they used, but said it was excellent. I've seen some of the vehicles of the first two on the list -- vehicles appeared in new condition and the drivers appeared to be professional & courteous.
And some others...
d) William’s Belize Shuttle, www.parrot-nest.com/belize_shuttle.html
William is based in San Ignacio -- don't know if he'll go to Mexico.
e) Discounted Belize Shuttles and Tours,http://discountedbelizeshuttlesandtours.com/index.html