If your procurement team secured a 10% discount, but the goods arrived 4 weeks after they were required so your client imposed penalty charges of at least that amount and maybe more, would you reward them with a bonus? Price is just one variable of a negotiation, I hope for your sake they at least know that.
Very good analogy. However on the flip side, you wouldn't be happy if they paid 120% of your budgeted cost because they rushed the negotiation.