Sounds like some settlement issues, but we need more info. How much is it sagging, the age of home, type of home and what are the posts and beams in the basement? Is there a concrete floor or dirt floor, and the type of weather you get? Full basement or crawlspace? Water in the basement?
Tell us a little more, or post some pictures if you could.
We are full of info....
Could be $1-3000.