Cost of joist sistering?

[Maurice D.]

hi, recently looked at two completed flips for sale, 1950's build on the same street.   both had weak flooring, that felt spongy, one significantly near the kitchen sink.

they rehabbed the rest of the houses great, but didn't address the floor?

Is this the norm? or does it cost too much to rip up the floor and fix the joists?

flip side of this :) , if I were buying the house, how much of a discount should I factor for the problem and will it pass FHA inspection ?