You shall increase the price in proportion to a greater number of years, or decrease it in proportion to a lesser number of years; for he is selling you a given number of harvests.
More remaining years mean a higher price, and fewer years mean a lower price, because what is sold is a number of harvests.
This verse explains the pricing logic.
13In this Year of Jubilee, each of you shall return to his own property. 14If you make a sale to your neighbor or a purchase from him, you must not take advantage of each other. 15You are to buy from your neighbor according to the number of years since the last Jubilee; he is to sell to you according to the number of harvest years remaining. 16You shall increase the price in proportion to a greater number of years, or decrease it in proportion to a lesser number of years; for he is selling you a given number of harvests. 17Do not take advantage of each other, but fear your God; for I am the LORD your God.