The music streaming business has become a rather aggressive one, especially after Apple joined the fray. Despite that, pricing for monthly subscription hasn’t substantially changed among the very few major players in that market. By now, the $9.99 a month fee is more or less standard everywhere. Amazon and Pandora, however, might soon have something different to say. The two companies are expected to debut new subscription offerings n the coming months, even as early as next week, that will be challenging the status quo and might give their rivals pause.