Square in the motherfarkin' marbles, for sure!
I don't know exactly what I pay because I'd have to do a pretty significant amount of math just to sort through paper cost, ink cost, initial cost of the printer, etc.
IMO, it's WAY better to print at home. The morons at the copy stores that a lot of folks here employ can barely do their jobs, let alone print your covers correctly. I've seen SO many posts where people can't get their local Kinko's/Copy Max/Staples to print these damned things at the right scale and on the correct paper. IF I had to deal with that kind of crap just to print a cover, then I'd probably be writing this post from prison.