In the event that any operator of a milk plant or distributor shall desire to obtain milk to be sold in the state of Rhode Island from any location outside the state, and inspectors for that location have not been certified or approved by the director, and it shall be necessary in order to make the milk conform to the requirements of this statute and the regulations promulgated to provide specially for the necessary inspections pertaining to it, the director may in the alternative either: (1) approve and certify an inspector specially for the purpose; or (2) send an inspector from the director’s own department for the purposes of making the inspections. In either event the milk haulers, the operator of milk plants, or distributors, as the case may be, requesting the inspection and the issuance of any permits involved, shall pay to the director all of the reasonable expenses and the salary pro rata of the inspectors not only of the inspection in the first instance incident to the issuance of permits, but for all subsequent inspections required by the director in the premises, the expenses to be allocated proportionately, according to volume, among the permittees requesting the inspections, if more than one.