This site has come a long way and their selection is almost overwhelming. Sizes of the prints vary and prices hover in the under $50 range. Most artists will produce prints in larger sizes upon request.
This is a site I use a lot at the office. It sells royalty free images for use by business and individuals. In fact, you can post your own photos for sale on iStock.
With this site, you are not buying a physical print. You are buying an image file which you can then print from your computer or take to a professional printer. If you are proficient with a photo editing software such as Photoshop or IPhoto, you can adjust color and change the image to suit your tastes. A 300 dpi XL photo file will run you about $15.
I found a link to the Savannah College of Art and Design's shop but I can't recall which site it was on (sorry to the source). It sells the work of the school's students and faculty online. Items range from jewelry and accessories to stationary to fine art. Most of the framed prints I viewed were in the $500 range.
Bird by Dan Saelinger. This is by far my favorite photo to date.