Is it permissible to exercise the right of pre-emption (shafa'a) over a piece of land that was sold, given that the sale was known and less than a year has passed since it occurred, and there is a dispute over its price?

If you are entitled to pre-emption due to sharing a right of ownership with your neighbor (such as a path or water), and you abandoned the pre-emption because the seller lied to you about the price, making it appear that the price was higher than what was actually agreed upon, then your right to pre-emption is not forfeited by that. You may take it for the real price for which it was sold, because your abandonment of it was for a purpose that proved to be contrary, and not out of a desire to relinquish it.