A quick Google search comes up with 9250 to 10500 is what is being asked for working ones.
Call a dealership and ask what a transmission is worth.
Then I would take the cost of the transmission off 9250. This would be my last offer if I really wanted the machine. My first offer would have my time to repair and general pia deducted as well.
If I got it I would try and find a used transmission for it as well to keep costs down.
Good luck.