"Rebadging" means Apple takes a drive (say for instance, one manufactured and sold by Sony), removes the front faceplate that says Sony on it, and puts it in their computers without a faceplate so you never know it's a Sony drive (unless you take the whole drive out and see a sticker on the case of the drive itself).
What he's trying to say is that you should find out what drive Apple is currently putting into the machines as a Superdrive (probably a Pioneer or Sony, I think they usually use one of either of those two brands) and buy the same exact drive itself. Then buy a 5.25 external enclosure with either USB or Firewire (or both) and put the drive in that case and you should be set, because the built in burning software in OSX will recognize the drive as a supported drive.
Here's a database to search for a supported drive.
http://forums.xlr8yourmac.com/drivedb/search.drivedb.lasso
No, the cost isn't changed whatsoever, but I guarantee that you'll spend less money on an internal drive + external enclosure for it than you will for a factory put-together external drive.