§ 258-a. Purchases by museums, historical societies, zoological gardens, aquariums, botanical gardens and arboreta through office of general services. Museums, historical societies, zoological gardens, aquariums, botanical gardens and arboreta which are chartered or incorporated by the regents or otherwise formed pursuant to § 216 of the state finance law; provided that each such purchase shall have a cost of five hundred dollars or more and that said museum, historical society, zoological garden, aquarium, botanical garden or arboreta shall accept sole responsibility for any payment of such cost due the vendor.