Meters for 220V plugs are
Meters for 220V plugs are expensive. Here’s one that attachs at the panel for $250:
What kind of controller do you have? Many of the new one’s (at least those based off Bartlett controllers http://www.bartinst.com/kiln.html) can actually tell you exactly what a firing costs if you program in the cost per kwh.
Helios Kiln Glass Studio