The worst possible scenario can be summed up as "Way to much!!".

That is a very large home and there are many things that can potentially be wrong with it!! At this point if you are seriously interested in the home I would highly advise that you retain a licensed Structural Engineer to perform an in depth inspection of the foundation and superstructure of the home. The Engineer can start with just a basic visual inspection and perform elevation measurements to see how much out of plane the home is from an expected level home. If it is warranted then you can move onto geological testing (soil sampling, etc.) to determine the potential for future movements. Geo testing can be quite expensive itself.

You need to take into consideration the other potential damages that could be there or could occur and all be hidden. For example damaged plumbing under a foundation can go a long time without being noticed. Depending on the degree of foundation movement you could also have damages to framing and other structural components.

Once the Engineer is done he can also create a remediation plan which you can now take to a foundation repair contractor for a proper estimate.

Good luck!

Emmanuel J. Scanlan
PS Inspection & Property Services LLC http://www.psinspection.com
214-418-4366 (cell)
TREC License # 7593
International Code Council, Residential Combination Inspector #5247015-R5 (Electrical, Mechanical, Plumbing and Building)
Certified Infrared Thermographer (ASNT-TC1A Standards)
Texas Residential Construction Commission, Third Party Warranty Inspector #1593
Texas Residential Construction Commission, Inspector, County Inspection Program
Texas Department Of Insurance, VIP Inspector # 08507061016
Hayman Residential Engineering Services, Field Technician
CMC Energy - Certified Energy Auditor

Knowledge is power, but sharing knowledge brings peace!!