I am not sure what we charge for the painting, but we always get a paint match in a spray can of enamel and spray them at the shop. Once you have a few sets to practice on, anyone can shoot a bunch of speakers pretty easily. 2-3 light coats, with about 30 minutes between coats and let them dry for 24-48 hours depending on temperature (do NOT try to bag/box them or install them before the paint is cured).

It does not take too much time. Unbox speakers, set them up on a table, prop up the grills on some dixie cups, spray them before you go home at the end of a day, let them dry overnight or more, and box them back up. I would say 1-2 hours of actual work for 6-10 pairs of speakers.