Congrats on the new rig, Sabretooth. As far as I know the Radeon HD 4850 uses GDDR3 memory so nothing particularly unusual or snazzy about its memory. From an initial search it appears there are a few of these cards that can be purchased for USD$100 or slightly less. If rumors are true though and AMD launches its next gen of GPU's in the next couple of months we may see more price drops for the 48xx cards before too long.
Also, if you're in India then what merchants can you purchase from? I don't want to quote some prices from different websites only to find out you can't buy from them. Q is pretty good at finding smoking deals though so hopefully he'll chime in with some recommendations.
What resolution do you plan/want to use when playing your games over the next couple of years? That will play a big role in determining what card you will need to meet your Very High/High quality graphic gameplay requirements.