I'd imagine the razors are sold at a loss, as Gilette know they'll be making most of the money back from blades/shaving cream. Seem to remember about half the boys in my class at school recieving free Gilette razors though the post on their 16th Birthday, leaving me (who had not signed up to the right direct marketing lists) feeling stuck in the realm of childhood until I recieved my free razor. I'm still there, waiting to become a man
I change the blades probably every two months or so, shaving every three days-ish. Not a hairy guy though so they're still usable even when I throw them away.