House with sloping floors

[Nat C.]

I viewed a house today with some serious sub-flooring issues. The house is built up off the ground and the plinths underneath are clearly collapsing. The tile floor inside is still in good condition but the floors slope up and down. Can anyone give an idea about methods and cost for fixing this? Can you simply add additional plinths to give structural support or does all the flooring need to be ripped up to rebuild the sub-flooring? The property could be a cash cow although the structural issues could also put a huge hole in the budget.