With no shop/warranty and possible tax on top of the asking price - that should be at $2900-$3200 max.
Everything sounds like an easy fix, but $4k is dreaming "as-is"...if there is not tax on top of the sale price, offer him $3100; if he says no, tell him to keep your contact info so he can let you know when he's ready to deal after he's held onto it for a few months and no takers