The furnishing of a performance guaranty in favor of the City of Port Republic in an amount not to exceed 120% of the cost of installation of improvements it may deem necessary or appropriate, including streets, grading, pavement, gutters, curbs, sidewalks, streetlighting, shade trees, surveyor's monuments, as shown on the final map and required by the Map Filing Law, N.J.S.A. 46:23-9.9 et seq., water mains, culverts, storm sewers, sanitary sewers or other means of sewage disposal, drainage structures, erosion control and sedimentation control devices, public improvements of open space and, in the case of site plans only, other on-site improvements and landscaping, provided that no more than 10% of the total performance guaranty shall be required to be in cash, and the balance shall be in the form of a bond from a bonding company approved by the governing body of the City of Port Republic. The City Engineer shall review the improvements required by the reviewing board which are to be bonded and itemize their cost. Such itemization shall be the basis for determining the amount of performance guaranty and maintenance guaranty required by the reviewing board. The City Engineer shall forward his estimate of the cost of improvements to the applicant within 30 days of the date of receipt of a request sent by certified mail for such estimate.