If you want to treat mold issue yourself, there is a way to do it for about $300 and it kills black mold. The chemical is called Spor-Klenz. It is used in clean room suites by Bio-pharmaceutical companies to create a clean and mold free atmosphere. it runs about $200/gallon and the rest of the cost is in PPE (masks and suits).

when you treat with Spor-klenz you will need to ventilate the area as it leaves a strong odor which is the active ingredient that kills the spor colonies.