My cable modem consumes about 10-20w (I’ve done monitoring). This while a single file server is continually backing up to Crashplan (about 700GB this month so far). So I don’t even see my cable modem in my power bill.
My file server is much worse - on average it’s consuming about 100w (or 2400wh/day). I’ve done the math several times, that’s about $1/day. It’s the box that’s syncing with all my devices, and then backing up to Crashplan.