In determining the cost of a project, the governing body may include all costs and estimated costs of the issuance of the revenue bonds; all engineering, inspection, fiscal, and legal expenses; any bond reserves and the interest that it is estimated will accrue during the    construction period and for six months thereafter on money borrowed or which it is estimated will be borrowed under this chapter; and the cost of retiring any existing indebtedness that the governing body of the municipality determines to be necessary or desirable and in furtherance of the public health or welfare, regardless of whether the existing indebtedness constitutes all or a portion of the cost being financed by the issuance of the bonds.