Lets see, no pictures, no ideas on why it's unstable, no way to tell how to fix it by just guessing.
It could be insect infestation, fungus ECT. we have no idea.
If the foundation was done wrong or the footing are failing then the whole house needs to be lifted and a new foundation needs to be built, and as stated $500.00 whould not even cover the materials.
If it's just some sagging that's a whole differant ball game.
Time to call in some pros and have them tell you what's wrong.
If the foundation is bad the whole house will suffer.