We use aftermarket ink, so it's like $45/liter, white, clear or CMYK. Since we're mostly a Mimaki shop, all the printers tend to have 2+ channels dedicated to white, so we can get a good thick pass and color on one go, it tends to be about a 20-30% up-charge. Then again, I just price stuff off the cuff and as of late, more jobs are fixing other people's printers than printing with them. So, my pricing may be way out of touch.
On some items, where it's full bleed, and we might have issues with adhesion, white spray or roll on paints are used instead.