I don’t think this portrait is any more or less priceless than the Crown Jewels. After all, the Crown Jewels are only a bunch of precious materials that an artist put together and have been associated with importance and uniqueness by (western) human history. Shakespeare is widely regarded as among the important artists in western history, so a genuine historic images would be important to many.

Now, people from other cultures may just consider both rubbish and melt down the Crown Jewels for the raw materials - or hang the portrait over their fireplace.

Priceless is always in the eye of the beholder.