Sometimes, pricing a work can be a real mystery to some. Many try to set up some kind of "normal work job type measure" as though they were working in a factory at GM or something. Well, it took $22 of raw materials, 14 hours of labor, and two hours of double time after midnight, then they divide by square inches and come up with... 
My head is spinning just thinking about it. A work of art is not

 a product. It does not get repeated and sold in bulk to a dealer like a box of cheerios. It can be measured only by the inherent quality that a the artist applies to it. That usually determines the cost. If the artist is realistic and keeps an eye out on the open art market, then he usually has an idea what a particular piece is going for, but the last word is ultimately the artists. A more successful work usually goes for more that one thats not. But this measure may not be apparent to the viewer. Only the artist. Works that match the intent of the artist and hit the mark are the ones you'll see higher prices on. Galleries know where the demarkations are on most works. Its their job. Size means nothing over accomplishment. A small work can rival a larger one if it " hit the bulls eye" so to speak. And then comes, reputation. You pay for "who" did the work. If Paul McCartney painted and sold a painting, it would of course cost more than if your old high school art teacher painted the same size and quality. To most, that seems unfair, and it may be, but thats the way it is. Brand names sell for more. Van Gogh was nothing at the time, but then became an "art rock star" after he went to the big easel in the sky. Now his name along will command exorbitant prices for even a so so rough sketch.
Also, experience, investment and dedication, track record of the artist involved and so much more. Its almost endless. Pricing the arts, is an art.
So the next time you ask an artist how he or she prices, remember, there's more to it than weighing a bunch of bananas at the market.