There's no way Rockstar spent 100 mil on marketing. Maybe 50 mil, tops, and it seems way less aggressive than IV's efforts. They don't even really have to advertise, all it takes is a few youtube vids and they can pretty much break even at a minimum from the pre-orders alone. Most of their ads are billboards, building murals and bus wraps so you're more likely to only see them in big cities anyway. They don't even do E3 or any of the gaming expos.
Plus, development costs were estimated around 137 mil in January right before its release date got pushed back almost 6 months, so factor in all of the additional employee cost and overtime on top of that.