Being the electrical kind of guy I am I keep track of my electrical usage in a spreadsheet. I heat the house with gas so my electrical average per day kwhr usage should be about the same as last year. The only thing that's changed since January 2013 is folding. Having just compared January 2013 billing cycle's usage to last month, folding's costing me about $1.62 a day.
I don't track natural gas usage like I do electrical usage but I hang on to my bills if get anal enough to go back and compare. But at any rate I'm pretty sure some my $1.62 a day has been offset by the heat generated by my folding gear!
8¢ per is pretty cheap for residential rates if you're factoring in taxes and everything else.