One thing that made our D’s study abroad costs higher, was the fact that she did some traveling. Not a ton, but enough where it added up. And of course the flights to and from Europe from the US.
Another thing that can eat up costs is going to visit your kid while they study abroad. If you’re really trying to watch costs, I’d say skip going to visit your kids. I think it’s fun if you can do it, but it’s not necessary.