Hi James, This would have to be from the Yuan dynasty, if it were right. And its value would be extremely high. Yuan blue and white porcelain is very expensive due to its rarity. Most pieces are in museums. It is so rare that during the following dynasties the existence of Yuan blue and white was forgotten; even the court did not know about it. It was only rediscovered in the 20th century, as far as I know.
Do I need to say more? Are you one of the few people who have access to such a piece? This kind of item is above me, I probably will never have an opportunity to handle one.
By the way, the photos are too small, and the color of the bottom is a bit off the norm, in my view.