Also, why does the title of this submission have quotes around "cheapest?"
I highly doubt it would be very effective, but it's not quite the same as a perpetuum mobile.
[EDIT] Though, after a little reading, it seems most supposed perpetuum mobiles tend to claim they harvest gravitational energy. That correlation makes your statement much more understandable.
"O speculators about perpetual motion, how many vain chimeras have you created in the like quest? Go and take your place with the seekers after gold."
Leonardo da Vinci
