Payment for the construction of said highway or highways, as provided for in section one of this supplement, shall be made by the county, which shall be reimbursed by the said borough, township, or incorporated towns, in such sums as agreed upon in said contract or contracts, upon presentation to them, from time to time, of estimates and bills for work already performed and paid for under the provisions of the act to which this is a supplement.
53 P.S. § 1832