Hi

It's not such a crazy idea. Using a balloon as a fuel cell reservoir has been suggested by a few people. The ion drive would need to be hoisted way, way up since they don't usually put out a lot of pressure - the atmosphere tends to smother an ion exhaust. Instead of an ion-drive you could use a magnetic sail and get a boost from the Earth's field - but such a big boost needs a current density that's maybe a few years away from being practical as yet.

It's not a crazy idea and really advanced systems might be used to mine the Jovian planets - they often have magnetic poles offset from their rotational axis by quite a bit which could have beneficial effects. For now though I'd put money on space-elevators for getting off-Earth cheaply.

Adam