The governor shall, within thirty days after it convenes in each regular session, submit to the general assembly a budget for the ensuing appropriation period, containing the estimated available revenues of the state and a complete and itemized plan of proposed expenditures of the state and all its agencies. The governor shall not determine estimated available revenues of the state using any projection of new revenues to be created from proposed legislation that has not been passed into law by the general assembly. Estimates of any unspent fund balances, without regard to actual or estimated revenues but accounting for all existing appropriations, that will constitute a surplus during the fiscal year immediately preceding the fiscal year or years for which the governor is recommending a budget, may be included in the estimated revenue available for expenditure during the fiscal year or years for which the governor is recommending a budget. As used in this section, new revenues shall not include existing provisions of law subject to expiration during the ensuing appropriation period.