Visiting the Great barrier reef

My wife and I plan will be visiting Cairns this July. We plan to visit
Green Island, spend a night on Fitzroy island and then take a trip out
to the outer reef. We have looked on the web and prices to the reef
seem to vary widely. For example, The Sunlover Cruise to Arlington
reef tour costs $155 while the Ocean Spirit Cruises costs $89. Both
seem to visit the same reefs and take about the same amount of time.
We are not interested in a lot of luxury etc (we are already spending
more for this trip that any previous trip) but this is probably a once
in a life time trip so I don't want to skimp on the essentials also I
do get seasick. Is there any reason not to take the cheaper cruise?
Has anyone taken one of these cruises? What did you think?

Also does it make sense to visit the reefs and both Islands or will
this be redundant?

Thanks
Steve Gerdemann
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