Is it obligatory to pay the price of the land to the paternal aunt at the current price, or at the price at the time of sale 30 years ago, knowing that she did not take the money then and said it was a gift or postponed taking it, and now she is demanding it?

If the woman told your father, "I do not want the price of the land; it is a gift to you," then this is a valid discharge, and she cannot demand the price after that. However, if she did not discharge him from the price and left it, then it is her right, and he must return to her the same price at which the sale was made.