For backyard porch columns, pressure-treated lumber is a good pick because it’s budget-friendly and stands up to rot and insects.

Have an expert look at it.I understand that you want to avoid setting untreated wood directly on concrete because the concrete attracts moisture that rots the wood. 

Sounds like you skipped cap-x and just took a hit of "hopeium" instead. ya, that stuff will rot your brain and drain the wallet fast. 

Definitely a very humid environment, especially near the coast, so expect to deal with all of the issues that come with high humidity - termites, bugs, mold/mildew, wood rot, etc.

There are tons of properties just sitting and rotting in downtown charleston because of this issue.

I don't have funds for the roof, or to replace the outside supporting wall frame and stucco.However the bank has changed the locks on me multiple times to "protect their asset", which got me wondering, would they also put a new roof on it and repair the rot to protect their asset?

That's what I think a fair price is.It does depend on how far it is to the roofing supply store, how far it is for the workers to travel, if there's any rotting wood that needs to be replaced and how busy they are (busier = higher profit).You could buy a couple ladders, a compressor, a 100ft extension cord (14/3), 50 ft of rubber air hose, a roofing nail gun, a caulk tube a couple shingle removers and pick up some day laborers who know how to roof. 

It could be as simple as bottle jacking a support or as involved as replacing multiple rotted beams and subfloor.

So, were these repairs where another problem (termite damage or rot) was hidden, or incomplete work on the contractors end like not putting tyvek under the siding or something like that? 

Long story short, cosmetically ugly and out of style is fine, not functioning isn't and WOOD ROT is a major no/no with FHA and VA appraisers.