Mont. Code Ann. § 7-6-103

The amount of any payment of sums in lieu of taxes may be based on the estimated cost to each political subdivision, for and on whose behalf the agreement is entered into, of performing services for the benefit of a project during the period of the agreement, after taking into consideration the benefits to be derived by the subdivision from such project, but shall not be in excess of the taxes which would result to the subdivision for the said period if the real property of the project within the subdivision were taxable.