Each regional council is empowered and authorized to contract for services of consultants to perform planning, development, engineering, legal or other services of a professional, specialized or technical nature; and such consultants shall be persons appropriately qualified under state statutes dealing with the applicable profession or occupation. Each such contract must have the express approval of the regional council or the executive committee. Such contracts shall not be subject to any law relating to public bidding: Provided, That every contract of the council for the purchase of merchandise, materials or supplies in the amount of $1,000 or more shall be let to the lowest responsible bidder after notice requesting such bids has been published as a Class I-0 legal advertisement in compliance with the provisions of article three, chapter fifty-nine of this code, and the publication area for this publication shall be the region in question.