TX/OK clay soil is less than ideal, and it's pretty standard to experience foundation issues with homes. that being said, the house is almost 100 years old and still standing. other than uneven floors, do you see any visible cracks by door frames (are all doors shutting properly?)

Also, both my phone ad tablet talk to me.

There is probably old wiring, cast iron plumbing, clay sewer lines and on and on.

Some of it depends on the area you live in, how deep the lines are, the types of lines (cast iron, clay, pvc, etc), and the soil types and such.For a job like that, you should get three quotes and have them try and break the quotes down by labor, parts, permits, and such.

Clay County or nearby. 

That job consisted of tearing into the old cement, pulling up a few clay pipe sections and a few lead pipes that connected to the shower, sink and toilet.

@Michael Clay in your situation, when you buy the property you would make sure that you convey to the seller that you might, in the future, sell the property and that you would like his permission to wrap his mortgage.

If your property is older and the gutter system feeds into an old clay pipe drain system it may have collapsed and you'll need to get those black accordian looking extenders. 

I've had to replace old clay pipes due to roots, but am surprised to get this call.  

For clay cass and platte they are all a bit undervaluing taxes but it is based on market value not sellable market value. in short estimate an increase of 5-10% for every property you are looking at.