The first of two 360 DLC episodes for GTA4 has been priced at $20. It's supposed to take 20 hours to complete. http://multiplayerblog.mtv.com/2009/01/22/gta-dlc-pricing-revealed/
Rockstar says the DLC will be more like full games than expansion packs... http://multiplayerblog.mtv.com/2009/01/22/rockstar-new-gta-episode-more-than-a-magic-hole/