(c) For each county eligible to receive a grant pursuant to subsection (b) of this Code section, the department shall calculate the approximate value of public services which the county provides the department each year; provided, however, that such sum shall not exceed the amount the county would charge any other landowner for such services. The department shall request funds in its annual operating budget each year to reimburse all eligible counties for the provision of such services. In the event the amount appropriated in any year is less than the amount requested, each eligible county shall receive a pro rata share based on the estimated value of services provided.