Yes, there are the obvious costs like the printing of the bill, the envelope and return envelope, and the postage to send out the bill - but there are also costs related to the labor to generate the bill, stuff the envelope, mail the bill, and answer patient inquiries about a bill.
There comes a point where the bill is small enough that it doesn't even pay to send it out, so KIP allows you to set a minimum amount to bill a patient.
To access this feature, go to File > Preferences > Billing Preferences and set the minimum amount to bill a patient. The default amount is $0.00. So, for example, if you set it to $3.00, patients will not get a bill below $3.00.
This way you can set your own preset amount as to minimum bill that you wish to generate.