(a) Contiguous Class I counties may join together and contract to create a joint county property appraisal staff. Under any such contract, the parcels of real property within the contracting counties shall be totaled and the counties shall be deemed one county for purposes of determining the class of the counties, the resulting minimum staff requirements, and the amount of money to be received from the department. The costs of the joint county property appraisal staff shall be shared, each county's share to be based upon the ratio which the number of parcels of real property in each contracting county bears to the total number of parcels of real property in all the contracting counties. Any number of Class I counties may join together to create a joint county property appraisal staff.

(b) Each Class I county may contract with a contiguous county which has a minimum county property appraisal staff to carry out this part. Counties contracting in this manner shall retain their separate character for the purpose of determining the class and minimum staff requirements for each contracting county.

(c)(1) Each Class I county, at its discretion, may enter into contracts with persons to render advice or assistance to the county board of tax assessors and to the county board of equalization in the assessment and equalization of taxes and to perform such other ministerial duties as are necessary and appropriate to carry out this part. The function of any person contracting to render such services shall be advisory or ministerial only and the final decision as to the amount of assessments and the equalization of assessments shall be made by the county board of tax assessors and the county board of equalization.

(2) No contract entered into pursuant to paragraph (1) of this subsection shall contain any provision authorizing payment to any person contracted with, or to any person employed by any person contracted with, upon a percentage basis or upon any basis under which compensation is dependent or conditioned in any way upon increasing or decreasing the aggregate assessment of property in the county. Any contract or provision of a contract which is in violation of this paragraph is void and unenforceable.