I've seen one with 2.8 mil go for 45k
If you're talking about the same one I've seen, though that was a legit fan page with a real website and everything. If it's just another BH page that will be eventually taken down it would be worth a lot less.
I think it totally depends on the business and whether the page is genuine, if it has a running business with cash flows etc, it can go for anywhere above 100k , again depending on the type of page, fan base etc.