Can anyone tell me how cad Raster to vector conversion will help to reduce my construction project cost?

I seriously doubt anyone here will be able to answer your question given the massive amount of information you've neglected to provide.Dave.

What is this "project"?  Is it a restoration?The only way I could see it saving you some time and money is if you had a set of original paper drawings for a building and no CAD file so you had it scanned then vectorized.  You'll still have plenty of cleanup work to do since the conversion is not 100% foolproof.