What is the "no appreciable cost" rule?

A local board of education can decide to transport students that live less than one mile from school.  If the district chooses to use the "no appreciable cost" allowance, and does not want to incur a financial penalty, the students must be transported at no additional cost which means the route cannot detour from the regular route nor can space be created for these students (5 CSR 30-261.040 (4)(B)).