301-72.3—What method of payment must we authorize for common carrier transportation?
You must authorize one or more of the following as appropriate:
(c)
Cash payments (personal funds or travel advances in the form of travelers checks or authorized ATM cash withdrawals) when the cost of transportation is less than $100, under § 301-51.100 of this chapter (cash may or may not be accepted by the carrier for the purchase of city pair fares); or