I cannot point to a particular vendor for submetering equipment as I am retired from the construction industry for 8 years and only moved here a year ago. Submetering is nothing new, it’s been around for 100+ years. Like most other tech, it gets cheaper, more capable and more accurate with every passing year. A simple Google search will show you a wide range of information on the subject. Manufacturers like Leviton, Eaton, Siemens, etc. offer a wide range of “billing grade” products to build out a submetering system. My only recommendation is to avoid small companies who want to be your turnkey solution. They tend to want to sell you proprietary systems and want to handle everything including your billing. You can well imagine how that often turns out.