(a) A contract in the amount of more than $15,000 for the construction of improvements or the purchase of material, machinery, equipment, supplies, or any other property except real property may be awarded only through competitive bidding after notice is published in a newspaper of general circulation in the district at least 15 days before the date set for receiving bids.
(b) A board may adopt rules governing the taking of bids and the awarding of contracts.
(c) This section does not apply to:
(1) personal or professional services; or
(2) the acquisition of an existing rail transportation system.