
Although the Sun does not generate a uniform amount of light throughout it's life and will continue to slowly brighten until it's death, about 5 billion years from now, we can still roughly estimate how much light will be produced between now and it's end and determine, in terms of energy costs, how much it would likely set one back to buy the Sun.
5.6216744275618786699008 X 10^40 joules of energy will be released in the form of light, by the Sun, in the next 5 billion years. Only one billionth of that energy will actually impact the Earth, so if our future successors require more energy, they might consider building a Dyson Sphere around our star.
This amount of eventual energy leaving the Sun can be converted to kilowatt hours (kWh) which registers:
1.561576229878299630528 X 10^34 kWh

If I were to expend this much energy at my home in the next month, the electric company would bill me approximately 2.1081279103357045012128 X 10^33 dollars, which although not very accurate for an estimate, people of today could reasonable expect to pay this, if the Sun were for sale.
I once heard that the combined sale price for everything on the surface of the Earth would be 1.0 X 10^15 dollars. That's quite a difference.