The promotion of proposed projects pursuant to the Statewide Economic Development Finance Act is a public purpose. The state covenants with the purchasers and all subsequent holders and transferees of bonds issued by the authority, in consideration of the acceptance of and payment for the economic development revolving fund bonds, that the economic development revolving fund bonds issued pursuant to that act and the income from the economic development revolving fund bonds shall at all times be free from taxation by the state, except for estate or gift taxes and taxes on transfers.