Yes, this is possible.
please note, for this to work the PC bios in question must have options for power recovery.
(i.e. what to do after power is lost. remain off, turn on etc.)
you can use a IP network power switch.
I cant vouch for any, as i have only seen other people implement them. its usually tower based servers, real servers have out of band management for this, in the form of a NIC and embedded GUI so even if the server is hard frozen, you can still shut it down / reboot.
You can find these on Ebay averaging around $50 U.S.
Set the Bios to power on after a power outage, when you leave the house put the switch in the off position via the administrative GUI. Then when you are out on the road or at a hotel etc, when you turn the ip switch back on your computer will power up.
I would think buying a WOL NIC would be the cheaper solution.