Joe,
Hood cleaning is not the best choice of words, the more accepted term is Kitchen Exhaust Cleaning or KEC which includes more than just the hood. Pricing varies on many factors (time since last service, access panels, filters, length of duct, horizontals, fans, how close can you get your machine to the kitchen, geographic region and many many other things). By code for KEC are you looking for the SIC, NAICS, UNSpsc and NIGP codes? or are you referring to NFPA? As for how many are in business, I know of 89 in the Greater Los Angeles area. Some may classify themselves as janitors but they are only fooling themselves, they are supposed to be providing fire protection services (and should have that insurance also)