Micro Enterprises has the capacity to produce 10,000 widgets a month, and currently makes and sells 9,000 widgets a month. Widgets normally sell for $6 each, and cost an average of $5 to make, including fixed costs. The monthly fixed costs are $18,000. Coyote Corp. has offered to buy 1,000 widgets at $4 each. What is the "cost" per unit in the context of evaluating the offer from Coyote Corp.