Braces are always expensive, and you are looking at thousands of dollars in work that insurance does not cover.
It depends on why he needs the braces. Don't be afraid to ask your dentist WHY he needs braces. If its for cosmetic reasons only, then of course, he doesn't need them. If he's a little worried about spacing...too far apart for example, he doesn't need them.
If he is getting chronic cavities because of his lack of spacing, then yes, you should get them. If his baby teeth are not aligned with the adult teeth that are coming in, then yes, he needs them because the adult teeth push the baby teeth up and out. The other option for this is having them pulled. Same for baby teeth that are in the way and need more space.
So you see there are lots of reasons and more why he might need them. Ask plenty of questions, ask to see the x-rays and for them to explain them, and it also never hurts to get a second opinion.
Good luck.