Courtesy of B&H Photo, I have been working with the Nikon AF 16mm f/2.8 fisheye (about $929). It’s a very compact lens, and what a great option to have along in a tight space! It’s so small in fact, that it can easily fit into a pocket.
A fisheye can be difficult so shoot (as I found!)— it’s important to find something to fill the frame without also grabbing pieces of bright sky, a tripod leg or one’s own leg, etc.
Of course, keeping one’s feet out of the picture can be a challenge.