I guarantee every single person on this forum has rattlecann'd something or other. Raw steel, paint them whatever turbo highspeed operator colours you like when they show up at your door. REAL pros know that you paint your gongs AFTER you hang them.
A good option might be to just make it an option on the website. "Targets come as raw steel - +$20 for painted"
If 70% of people as indicated by this poll want it raw anyway, you could end up saving time not painting targets you otherwise would have given a quick spray job by default. Then only bother spending the time on it for people that really want it and are willing to pay for your time.
Even left out to rust our targets (edit: and stands) will last a lifetime, A is running a fun experiment leaving some 3/16 in lye for a few months just to see how the wear and tear goes.