PoBoy... my advice... for the first month, go for the plan that you have stated (256kbps, 500mb limit). by the end of the month (i.e., around 25th), change your plan to the 64kbps unlimited (Rs.500) plan.
@poyboy dont go for any data limited plans you will repent later when you see the bills. go for a data unlimited plan, if they dont have one look for another isp or be happy with dial up.