There is a project written in borland builder c ++ 6.
It is required to alter the code under msvc 2015, i.e. essentially do refactoring.
The amount of code is known. Let's say a total of 3 MB (this is without resources: icons, pictures, etc. - pure code).
Tell me, what are the best practices for determining the lower limit of the cost of refactoring (in any units: man-hours, monetary units - whatever).