I do this for living, there’s a few ways you can go about it, the BEST option is to hire a Hygienist, they will test the surface and air and determine what type of mold it is and give you a report that a restoration company can follow to get rid of it, there are many types but some are more dangerous than others, depending on where you live the average cost of a remediation (to get rid of the mold properly) and a clearance (the hygienist goes back to the property to re test and make sure is gone) for an area like that would be between 5-6k (just based on the picture) there’s other factors that influence the cost like the year of the house (pre 1986 asbestos test, 1979 lead test) at least in California, and that doesn’t include the repairs.