If you contact a foundation repair company they have a material that they inject under the concrete that will raise it up even, then you just have a minor cement repair that can be masked with a rough finish on the entire porch.Or remove it and put in a wood porch.

He would be replacing the cement board as well. 

What attracted you to them and what cemented the decision to move forward with them?

There should be plenty of framing to attach drywall or cement board to.

I'm looking at an REO property that is a pretty cosmetic flip except for one thing: HUGE cracks in all the cement under the flooring.

What we typically do is either lay 1/2 ply or OSB over the planks screwed into the joists w/ 3-inch deck screws, then put a standard waterproofed cement board thinset tile installation in bathrooms and kitchens.

also need  cheapest source of cement in bags for part of this place. 

The room used to just be a leaky storage space with crumbling wall cabinets and peeling cement ceilings.

I usually skip the underlayment with laminate and skip the cement board with tile as well for additional savings.

I still don't think underlayment matters much except maybe over concrete because of moisture and I'll put tile over plywood all day long unless it feels bouncy then chances are it will crack without more plywood.My thought is it says I can put it over plywood on the bag of modified thinset so if the floor is solid then why spend the extra time and money on cement board if I'm using 0.49/sqft tile anyway and doing it myself