Who are you booking it with?
We have used Belize Cruise Excursions: http://belizecruiseexcursions.com/Lamanai_Belize.htm
for this tour and it was great! The wildlife was amazing on the river and the ruins are a marvel.
It is a long tour so don't expect to have a bunch of time at the end to shop at the port. We picked up a few tshirts right at the ruins site and locally made jewelry. Our guide was really entertaining...can't for the life of me remember his name..very different, sorry