Re-rolling a subgrade that failed its density test costs more than renting the roller that would have passed it the first time. One failed density test costs more than a full week of roller rental. Suppose a used 54 inch padfoot roller runs $42,000, financed over five years at a payment near $780 a month. On a $13,000 carrying cost against a rental day near $300 delivered, that is roughly 43 days a year on one machine. Track cost per machine hour for a single season and the decision stops being an opinion.