You can by the 10w0 sub for $99 anytime brand new. Considering his is used (and you can press in on the cone a few times to see if the sub moves VERY freely or not; if so, its probably been played ALOT), I would offer him $50 for the sub and box. Don't let him pull the old "this is a custom box that cost $$$$ to build; remember, it is custom to HIM, not to you. You might even act as though you don't think the box will work in your car to see if he will accept the $50.

Otherwise, I'd pass......