Cheapest solution is as Reno said: Check meters, or sub-meters...IF they are allowed in your locality.
Hassle is someone has to 'read' them and process the billing. And someone has to be responsible for the 'main' POCO meter & paying that bill. Yes, there are co's that do the 'paperwork' (for a fee). There are also other mfg besides E-mon.
Need more info?