No local government shall evade the provisions of section 2308 (relating to bids for certain joint purchases) as to advertising for bids or purchasing materials or contracting for services piecemeal for the purpose of obtaining prices under a base amount of $18,500, subject to adjustment under section 2308(b), upon transactions which should in the exercise of reasonable discretion and prudence be conducted as one transaction amounting to more than a base amount of $18,500, subject to adjustment under section 2308(b). This provision is intended to make unlawful the practice of evading advertising requirements by making a series of purchases or contracts each for less than the advertising requirement price or by making several simultaneous purchases or contracts each below such price when in either case the transaction involved should have been made as one transaction for one price.