They will cause constant issues like clogs, electrical shortages, lead citations, remediation if there is asbestos in piping or building materials, etc.Maintenance and CapEx are your two most variable expenses.

Does anyone have recommendations for a cheaper remedy ?

Would the remediation affect the top unit that has no mold or problems at all?

Found what was wrong with the property during inspection, had multiple contractors quote remedies, and leveraged it to a large credit at closing that paid for the down payment and a check to us!

Your best bet for mold is to get a mold remediation company out to deal with it.

There could be other unseen environmental risks that the old phase 2 did not remediate or something affecting the area since 2012.

You suffered a loss to your property, they need to pay to remediate.

The initial numbers I ran did not take into account remedy the crawl space issues so I would need credit on it to move forward.

Now that they know about the mold and damage, they ethically have to disclose it to all future buyers.I would get some quotes on remediation and repairs, then negotiate the price accordingly. 

Most folks use home remedies (i.e., boiling water poured down the mound) or any one of the chemical treatments the big box stores have to deal with them.