10" sub.... 500 price barrier....

I wouldn't pay too much attention to the power of the sub. The sub will be designed with an amp that will be fine with it, at least up to crazy levels. And if you are mainly listening for music, you will be fine. Instead, for music find a sub that will integrate well with your main speakers. REL has always excelled in that area. I loved my Storm III when I needed a sub. But even if not REL, the question you want to be asking is about integration, not power.