The plans arrive in December. Until then, everything is free.
The prices are decided, and they are announced in December. If your guess for a plan is within ten rupees of that plan's price — above or below — that plan is yours for a month, free. If more than 300 people land inside the band for one plan, the earliest 300 win. One guess per account, made from the extension. The prize is a month of the plan, not money. Zeya sets the prices; guesses do not change them.