The purchasing agent may make additional purchases of supplies, materials, equipment or services from a successful bidder, provided that:
(A) Amounts of additional purchase are at the same cost or less per quantity as originally bid by the vendor;
(B) Amounts of additional purchase do not exceed the cost of the original purchase;
(C) The purchase occurs not more than 12 months after the date of the original purchase; and
(D) The purchasing agent is reasonably certain that the same supply, material, equipment or service is not available at a lesser cost from any source.