Calculate the margin on this short$-$the$-$basis transaction:

Make a sale of wheat to a mill at $+15$ DEC for Oct$/$Nov delivery.

Purchase wheat from farmers for delivery direct from the farm to the mill at $-15$ DEC during October and November.

Farmer delivers grain using his trucks. No freight cost to you.

You are paid by the mill upon delivery and in turn pay the farmer resulting in NO cost$-$of$-$carry to you