reproduction of flat art can be difficult to do well.  there must be twenty ways to mix the same brown with acrylics, and each may reproduce differently.  In the old days it was a wise artist who struck up a relationship with his photo lab/graphics house, and painted all the colors as individual swatches s(he) used in painting, particularly acrylics, and gave it to them for reproduction, and which colors were true to the original were noted, and those that deviated could be identified and possibly used less.  architects and graphics artists use graphite and felt tips too which all have eccentricities.  it was often an experience no one enjoyed.       When the digital tool case was good enough to take its place in pro graphics, dealing with illustrations of all kinds is manageable ... not a cakewalk, but do-able.  read more here.

up to 8 1/2 x 11 is done on a flatbed scanner.	$25
larger sizes can be scanned in sections and spliced in a photo-editor, up to 11x17	bid
larger sizes sometimes require a camera of suitable resolution, and sometimes those are done in sections and spliced later ... it all depends on the subject matter.	bid
on the rare instance where a color transparency larger than 4x5 is concerned, we use a local vendor employing a drum scanner.	bid

the amount of time necessary to make final color and value adjustments, and the charges for same are not known from the proof which is made at time of scanning, that needs to be done when the printing stage begins.  large deviations will be visible in the proof, but subtle stuff requires the scrutiny of the final printing step.