The artist actually decides on the selling price of his artwork, but this decision must get the gallery's approval before it is showcased. An artist must make the final price seem reasonable to the buyers by basing it off of the realistic efforts in making the piece.
A common mistake made by many artists is determining the price of the work by how beautiful they think it is, how emotionally attached they are to it or other unrelated personal factors. Artists are better off keeping the artwork for themselves if they are that attached, since prices determined for such reasons often discourage galleries and lead to haggling.
Instead, an artist should begin by keeping track of the time and materials required to make the piece; an artist could set a realistic hourly wage based on how much effort he puts into the piece and add the price of materials used in the process, especially if refills of paint and ink are required.
Another option is to attend other galleries or auctions; an artist may take notes on how much he sees collectors willing to pay for similar pieces of art, work out an average, and place his or her price within that range.