It looks a little confusing in the planner, but cabana prices are per cabana and not per person. The best deal I've seen for a cabana is $399 on the special sales like Black Friday, but more commonly see $499 when they are on sale. The beach club ones are $799-$1199 as the best price I've seen. You can cancel and rebook if the price goes down and even with the other recent cruise planner changes, you can see the price if it is less than what you paid. I have the over-the-water cabana booked at $1199 (was $999 on my cruise that was cancelled last year, probably getting cancelled again). Looking at the new summer sailings, the prices are insanely high! If I was cruising then, I would just stick to the free stuff!
We enjoyed our water park cabana because my husband and I sat and relaxed while our kids climbed the stairs for the water slides dozens of times! We have also just paid for the water park without a cabana and we got lucky that day because it was cold and rainy! We didn't stick around as long as we would have otherwise.