We have a minimum charge for all orders -- with the provision that you can use up the excess between the minimum charge and the actual amount of your order on one additional order.
We have this minimum because it takes us a certain amount of time to start and finish each order. These are the tasks for a typical order:
As you can guess, steps other than 4&5 eat up a lot of time that we do not get paid for. And, small orders take up the same amount of time in steps 1-3 & 5-9 as do large orders. For this reason, we have a set minimum for all orders.