Ask HN: Anyone know of a 3rd party Product Manager,billing, invoices?

Looking for something that can manage all of our products, purchases, and invoices. We do not have many products, but we do have an insane billing structure. Where their could be tax, adjustments, Affiliates, Affiliates that get adjustments, promotion codes, initial product subscription price, subscription price. ect. If possible the system should play nice with paypal payflow pro. I'm currently writing a custom one which will work out fine. But the boss wants to know why im writing one when their seem to be so many other solutions. My answer was finding one that meets most of our needs will be hard. And by the time we set it up and integrate it into our system I will probably be done coding one.