I don't have a dollar amount in mind, but I'd go to at least a c-note each.
Of course, my first act would be to come over here and extort money from the posters on this board to start a thread doling out details a bit at a time. Say, $5/answer. I figure I could break even on the deal (especially if I charged $10/answer for word for word quotes . . . )
If Le Rouse came up to me today with a 4e PHB in his hand and said it could be mine if the price was right, I would probably dish out upward of $350 for the thing. I wouldn't buy all the books, just that one, but I would pay out the nose for it.
You hear that Rouse? You know, just in case you're reading. I wouldn't tell anybody. <_<
As a gamer, I wouldn't go for more than cover price. I'm too busy with current 3.5 campaigns that I'm not even sure if I could start 4e when it comes out. I am curious, but I can wait.
However, as a freelance writer, I would pay at least double cover price and possibly more. In fact, with Wolfgang Baur's Open Design, I did exactly that in hopes I coudl get some sort of access to the rules to learn them early. Of course, even with that I still won't be getting them tomorrow. (C'mon, WotC, finish that GSL!!! )