To plaster the cost is per surface area A wall 10 high x 10 ft long is 100 feet x 4 walls 400 minus window area.

This is just my example of what a small, independent brokerage can offer and really doesn't even scratch the surface.

The access was in my bedroom and every surface was covered in a fine dust.

Always aim for surfaces and colors that feel clean, non-busy, and low/no maintenance.

ALSO another thing to keep in mind:  this is only what the inspector can see on the surface-  when you have a ton of items like that that are visible just consider the things that he could not uncover with his inspection. 

On the surface it looks like a decent deal. 1.

I've built a 3000 square foot, and a 5000 square foot.Had to pay for a geotech engineer, a civil engineer, an architect and a drainage expert due to site problems.  

Now clients would want level 5 wall finish (smooth surface vs textured) which takes 3-4 times longer; paint would have to be super sharp on color transitions (1 coat primer, at least 2 top coats); all baseboard and trim work & paint have to be perfect: no brush mark, no visible nail holes etc;  and all everything else in between.So my point is: beside using your elbow grease to gain sweet equity, pricing is subjective to quality

What lurks below the surface can really crush a project.  

Nearly every surface in the house will need to be touched, and in some cases gutted down to the dirt.