As a distressed property general contractor, RE broker, investor and property manager who has been specializing in mold remediation, rehab foundation, drainage and structural issues for 3 decades I'd have to agree with Johnathan.
When we are contracted by a homeowner to repair mold related damage we never give a firm quote. It's always done on a T&M basis or we don't sign a contract. I'd rather walk away from a deal than be plagued by it and worse to lose my shorts on it.
You just can't determine how much damage has been done i.e, drywall, paneling, plaster, insulation, structural components i.e. framing exterior siding and even fixtures and appliances, etc. until you've done a thorough inspection.
This generally involves a certain degree of destructive inspection which you would be responsible of repairing unless the homeowner, bank, law firm or in some cases insurance company is willing to pay you to do the reparation of the destruction you had to administer in order to determine the degree of damage.
I've had decades of hands on experience doing these types of repair projects and many of them have ended up costing tens of thousands of dollars. Some have exceeded 50k because as we got into the project we kept discovering more and more damage i.e. dry rot, framing deterioration, decomposition, etc.
Not trying to make a mountain out of a ant hill but these things happen more often than not. So trying to determine the ARV on a mold issue is a lot more complicated than just stainless steel appliances, new flooring, granite countertops a paint job and a new lawn which are all fixed costs that can be easily factored into an F&F..
What you think can be a clean 50k ROI could end up costing you your shorts. Take the advice of those who suggested that you get a licensed, bonded and insured mold remediaton specialist to do a complete and thorough inspectin even if it cost you a couple of grand for some rudimentary destructive inspection. It will probably be the best investment you could make on this property. Just sayin..........................