Major mold issues

Here is the story. We know of a house on Probate not listed anywere yet. It is a very new probate proerty. My husband and i know the person that lived in the house and the children too. We would like to make an offer on this supposidely nice house. There is no mortgate on the property now so we can probaly get it for a real steel.
From the outside it seems really nice. However my husband looked at it yesterday turns out it needs some major repair such as windows and doors and a new roof on garage and house. This is not the major problem in the property. The major problem is Major hazarduous mold. I know that servepro is a good company for this kind of thing and we do have several in this area. The basement has slimey green mold i dont know if there is any black mold in this. The mold comes from the fact that the basement floods anytime it rains alot so we would also need to redo the basement from floor to cealing as well. I was thinking that we could offer really low at $15,000 or $20,000 but am not sure how much a major mold clean up would cost or if it is worth offering. Should we offer on this property? What would any of you long timers do? Please help!