As a fine art photographer I had to deal with this issue. There are a lot of not-so-obvious factors besides size and quality of the print. You have to know your market: who would buy it? Some of my photos were bought simply because the colour matched their decor! You have to do some market research as to what similar photos are selling for. I often went to photo galleries to set my price expectations.
Where you sell also affects the price: a $1000 price on a photo displayed at the local cafe will probably not sell, but in New York or Maui it may.
Of course your name and reputation are important - A small Ansel Adams photo may sell for much more than a large, high-resolution, well-printed, well-framed photo by an unknown artist.
Bottom line: look at the prices of other photographers' work and decide where you fit in.