The lumber to repair the wall studs should cost around $200.00 but the cost of labor is what's gonna cost the most.
The contractor will need to jack up and support your walls most likely from the outside using posts. Then they'll cut out and remove the old wall studs.
They'll have to remove drywall or plaster whichever you have to replace the wall studs so that will add to the cost.
If you can remove the drywall before they do the job of replacing the studs then you can save some money.
Replacing the studs might take 8 hours or more depending on how many wall studs need replaced.
You might also need to replace the Sill plates as they're most likely water damaged as well. This will require more work and you might have to remove part of your floor to get at this.
Expect to pay $800.00 or more to replace the wall studs using a contractor. And always expect to pay more as you will most likely end up finding more problems once you open up the wall.