(a) Except as provided by Subsection (b), the commissioners court shall purchase the equipment, materials, and supplies for the county road department through competitive bidding in conformity with estimates and specifications prepared by the county road engineer.
(b) If the county road engineer so recommends and the commissioners court considers it to be in the best interest of the county, a purchase in an amount of $50,000 or less may be made through negotiation by the commissioners court or the court’s authorized representative on requisition to be approved by the commissioners court or the county auditor without advertising for competitive bids.

(c) A purchase may not be divided or reduced to avoid the competitive bidding requirement on a purchase that would otherwise cost more than $50,000.