Welll, minimum 45, but most likely 48. What if you wait several scout lists and still no AMC/AMR with shadow that you want. You are willing to pay 50 tokens, but it never hits your list and rarely goes cheap on the transfer market. Neg for 45 tokens would be the smart thing to do.
Still, I'm not letting this guy go for 20 tokens, or 45 tokens.
I think there should be a minimum amount of tokens offered when you first make the offer, so there are no zero token offers.