Refunding bonds issued pursuant to this article may be exchanged for the bonds to be refunded on such basis as the legislative body determines is for the benefit of the local agency but in no case on the basis that the principal amount of refunding bonds exceeds the principal amount of the bonds to be refunded plus the costs of issuing the refunding bonds. As an alternative to exchanging the refunding bonds for the bonds to be refunded, the legislative body may sell the refunding bonds at public or private sale for not less than their par value. The proceeds of any sale of refunding bonds for cash shall be placed in the treasury of the local agency to the credit of a fund to
be established for the purpose of refunding the bonds to be refunded, which fund shall be designated the “funding fund,” and such proceeds shall be applied only as permitted by this article.