Inspection Contingency and Known Defects

[Rick Richard]

I'm ready to sign an offer to purchase on a property that has water in the basement/foundation cracks.  The offer includes an inspection contingency. The contingency states Defects do not includes those the Buyer had actual knowledge or written notice of.  (I do have written notice of with Condition Report).  My question is if inspection turns up foundation damage will cost much more than what I expect and budgeted for...  E.g., will cost $20k, when I estimate $10k.. may I legally void the offer after the inspection? (assuming Seller will not cure).