What is the value of a photograph?

When it comes to art or creativity it's subjective. And art is only worth what your willing to pay for it. One person's monthly income is another persons pocket change. Personal style, preference and tastes vast dramatically from age, culture, social groups and geolocation. So can one find a baseline for what a photo is really worth to the user in today's economy? And answer the question, what is the value of a photograph really worth?