That sounds like a good idea,
My room is 12'x10' with only 2 plants in veg and 700 watts of total heat dissipation (including Dehumidifier).
I have a Kill-A-Watt meter on both the AC & DH, the AC has used 11,000 watts in the last 6 weeks costing only $11 at my rate of $0.10/kWh, I lost the data on the DH but it was only running half that of the AC. We have been in the high 90's with 70% humidity since I started this grow, keeping the room at 77F @ 45% rh.
If you're gonna buy a Kill-A-Watt meter make sure it is the model that retains the memory during a power outage #P4460 about $25 at walmart, the cheaper #P4400 works well but will not retain memory when unplugged.