Snorkeling in Fiji

I will be in Fiji in February and staying on Denarau Island at a friend's time share. I want to do some snorkeling as a day trip. Any suggestions for where to go and what companies offer good trips? I saw one called Whale Tale which offers a day trip for about US$100. I was hoping for something less expensive but the quality of the snorkeling is most important. Any suggestions will be greatly appreciated.