I've had mixed experiences with fruit in general since coming to America. I've found that the prices, in general, are similar to those in America, but you get a lot more for your money here. If you have a family or are a big fruit eater, this is a good thing. If you're the only person who eats a particular fruit, such as, watermelon in my case, then paying $5 for a big one means that you're either throwing away some of it or force-feeding it to yourself for an extremely long time.
The truth is that the sizes of food in Japan tended to suit me better. I guess that, if I didn't mind wasting food or cramming enormous melons into my refrigerator, I'd be happier with the size of fruit in the U.S. As it is, managing the (usually) mammoth melons is annoying enough that I rarely buy them at all. I miss those compact little melons.