Private boat tours will cost more say over $100US easy.
Some group tours are offered for more reasonable costs. ie Amigos Del Mar & others.
Ferry to Caye Caulker or take a catamaran group tour & snorkel and see the island. Just different lengths of time on island or sea.
Also, I rent a golfcart for at least one day the price is worth all the adventuring you can do by yourselves - we take it to snorkel from Victoria's dock all the way north to other rest stops!
Also what tour do you want besides outer islands?
We had a great shore lunch on a Bird Caye sanctuary & it was awesome.
Belize it!