Any public agency entering into an agreement pursuant to this act may appropriate funds and may sell, lease, give, or otherwise supply the administrative joint board or other legal administrative entity created to operate the joint or cooperative undertaking by providing such personnel or services therefor as may be within its legal power to furnish: Provided, That the board of county commissioners of any county having a population of not less than forty-two thousand (42,000) nor more than fifty-eight thousand (58,000) with a total assessed taxable tangible valuation of more than eighty million dollars ($80,000,000) may use the money heretofore or hereafter collected from tax levies made under the authority of Kan. Stat. Ann. §§ 19-1569 and 19-1570, or acts amendatory thereof to pay the county’s share of the cost to provide for the acquisition of building sites and parking areas, design, construction, furnishing, and equipping of a combined unit of courthouse, city hall, jail and parking facilities in cooperation with the city which is the county seat of such county.