Don't forget the all important disclaimer. No point in getting the job, working your nuts off and then losing all your profit and more because you picked up some manufacturing debris, or sand in the mortar splashes and scratched the nice new glass.
As to price: at least 3 times what you would quote for a normal clean, but have a good look first, if there's lots of scraping to do, multiply that by another 2 or 3.
My opinion? Builders cleans aren't worth the hassle. Let someone else get the headache.