No clue about the S/N but your NH dealer might be able to help w/ that. Not sure the $4k price is that much out of line. Price really depends on locale, condition, how many bales thru it, if it was properly maintained etc. If the guy youre buying from has run it and doesnt know what he has then my guess is he also didnt take great pains to maintain it. This is NHs current low end baler...