sorry about your plight. this sounds like a wood frame Bungalow house built between the 1910's and 1950's, or wood floor framed block home built in the late 1940's or 1950's, here in Clearwater. we (Architect) were contacted by another recent Homebuyer who found similar items, but they were able to contact the previous Homeowner and came to some financial agreement on the repairs. you may want an inspection by another Home Inspector (many of whom are retired Contractors), or better yet a Structural Engineer who will crawl under the house.
on the Bungalow homes, which typically have wood beams and piers that sit on individual concrete footings, the footings & piers may also need to be "straightened" because of 100 years of rain and wind, or replaced due to rot (not often, since they were built with heart pine).
or, as another commenter said, it may indeed just need the subfloor replaced, but i'm guessing there is a water leak if it's just rot - roof leak or burst water pipe under the floor. we have also found that people have removed or replaced old mechanical floor vents (18"x24"), which ends up with a soft spot because there are no floor joists there.
finally, you might want to look up any permits that were pulled for the property.
https://www.myclearwater.com/g...
you can email me for a Structural Engineer referral if you would like. good luck!