a. All purchases, contracts, or agreements, where the cost or contract price exceeds the sum of $25,000, or, after January 1, 1999, the amount determined pursuant to subsection b. of this section, shall, except as otherwise provided in this act, be made, negotiated, or awarded only after public advertisement for bids therefor and shall be awarded to that responsible bidder whose bid, conforming to the invitation for bids, is most advantageous to the commission in its judgment, upon consideration of price and other factors. Any bid may be rejected when the commission determines that it is in the public interest to do so. Any purchase, contract, or agreement, where the cost or contract price is less than or equal to $25,000, or the amount determined pursuant to subsection b. of this section, shall be made, negotiated, or awarded by the commission without advertising and in any manner which the commission, in its judgment, deems necessary to serve its unique interests and purposes and which promotes, whenever practicable, full and free competition by the acceptance of quotations or proposals or by the use of other suitable methods.