Wow! Thats about the amount they use to make films with! Rockstar have put alot of effort into this game as they do for all their games and I'm very happy to hear it.
Source: http://www.psxextreme.com/ps3-news/2978.html
F-ing hell! $100m - thats loads of cash!! Just to put it into perspective, here are some things to compare it to
Lord Of The Rings movies: They cost $99m EACH on average (2001 / 2002 / 2003)
The Lost World: Jurassic Park - $75m in 1997
James Bond: Goldeneye - $60m in 1995
GTA IV: $100m
I think Crackdown was just under $50m and Halo was around $60m - but thats just from what I've read in the past, it may not be true.
Its bound to be worth it though, it is a masterpiece. I hope they can make enough profit to continue making GTA games!
I bet it is bro. A tru masterpeice it is.