Time of year advice

We are going to be visiting Maui, kaua’i and the big island. Currently, we were thinking of going end of February and beginning of March. However, I keep seeing how the weather is better in the spring and technically we could go whenever we want. I would like to see lots of whales though. I thought one time of the year was supposed to be cheaper than others, but no matter what I look at. It seems that the costs are about the same. I’m finding out a little confusing.