Depends what he knows. If he only knows a new one at the dlr is $300, then I'd say at least $200.
If he knows stock M7 pipe takeoffs are dime a dozen, then I'd say hope for $100 and throw in some springs and the muffler bearings!
I've had 3 different stock exhausts for popular sledz and haven't sold any of them. Threw 2 away when I moved last cuz I was tired of moving them.