No, it doesn't reverse so easily. "I'm 20 dollars out" means "I'm $20 out of pocket." If you say "I'm $20 in", I guess you've joined a game of poker. Even then, I wouldn't use that phrase. If you picked up $10 from the street, then it makes more sense to say, "I'm $10 up" (again, hardly my first choice of comment for that situation).
"I'm 23 pages in" means "I'm 23 pages into the book." The opposite to this would be, "I'm 23 pages from the end (of the book)."