A fresh Mountain Lion install, without any of the iLife apps or anything else, should be about 15 GB. (Of course, that's on a mid-2010 MacBook Pro... it's possible that number will be slightly different on a new retina MBP.) With iLife, it will, of course, take up more space.
You need to stop removing things from the system, especially using tools like Monolingual to chop bits out. That can cause certain applications to fail to be updated in the future or to stop working entirely. You could reinstall ML fresh, without iLife apps, to reduce the size a bit.
However, if you're finding 256 GB so tight that 30 GB is too much, you should probably return it and get one with a larger drive.