Based on Kelly Blue Book price for a 94 in excellent conditional is valued at $3100.00. So price is high.
Now as I make my living as a buyer any item is worth what somebody is willing to pay.
If taken care of 250K miles on the 6 cyl. cummins should be no problem. If a "new trans" that's good news.
If your comfortable with it buy it.
I would give him $2K. but I'm the guy that spent $7K for a 99 F550 with 228K miles and a trans rebuilt in 2008. Paid $2K a year later for a ford reman trans when the rebuilt trans failed. Still into it for less than it's valued.
Just my 2 cents