You could borrow my hangtag since I'm only going to be at school for a couple hours tomorrow. :) GMU is a few blocks down from the Virginia-GMU Metro Stop. Or you could go to Pentagon City and take the metro from the basement of the mall. I'm not sure how much the parking is at the garage at the mall. It's a couple dollars for the first hour but I don't know what the max is.

Parking at a metro station is $3.75 but you have to have a SmartTrip pass to get out of the lot. I'm not sure how much it costs to get one (K gave me mine for my birthday) but you could always borrow mine. And pay me back in brownies. ;)