(a) A purchase may be proposed on a lump-sum or unit-price basis or a combination of a lump-sum basis and a unit-price basis.
(b) If a district uses unit pricing in its notice, the information furnished proposers or bidders shall specify the approximate quantities estimated on the best available information or other quantities reasonably specified to permit comparison of proposals or bids, and the total contract amount may be based on estimated maximum quantities, but the compensation paid the bidder must be based on the actual quantities purchased.