Pricing artwork is a difficult science at best. Many factors influence the price of a piece of art, but the key factor is of course demand. The more collectors want work by an artist, the more they are willing to pay.
Supply is also a strong factor. Usually emerging artists' prices are a fraction of what established well-known artists can obtain. Auction prices can vary wildly from gallery prices, depending on the bidding.
We usually set a price on the basis of what think is fair market value, plus a selling record, accounting for size and media, and then discuss it with the artist.