I am heading to Cairns, Australia for several days and wish to spend
two days taking day-snorkling trips that depart from Cairns (as
oppossed to Port Douglas).  One of these trips should include Green
Island.

My own research indicates quite a variety of tour operators, but I am
at a loss as to which ones are most reliable and offer the best value.
 I am not seeking 5-star elegance, but do wish to be sure that I am
comfortable, safe, and that I receive what is advertised.  Rates that
I see range from AU$90 - AU$190.  Am I getting better basics with the
more costly tour, or just more upscale amenities, that are less
important to me.

I am looking for reviews, personal experiences, and comments about the
quality of these operators so that I can make an educated
selection....Thanks!