I have some mp3s for sale. Some are for free and some need to be paid for. Now, what I would like to do is change the products, so the free mp3s are only available if someone buys mp3s for at least 10$. Is that possible without doing discount codes or such things? It would also be cool if like 5 free files could be packed into a package product and this package would be added automatically if checkout is >10$. Any way to implement this?