Notwithstanding the fact that no disbursements may be made during any fiscal period in excess of the appropriations made available by the General Assembly for the fiscal period, it is provided that contracts for improvements including major repairs, alterations, and construction of new buildings and facilities may be let to the extent of the appropriations made available for those purposes for the biennial period. However, no such contracts may be let in amounts exceeding the probable funds available or which are estimated to become available during the period.