I'm interested in the Lensbaby Scout since it seems like a cheap fish-eye option, but I am unsure how it performs. What about the lens's quality (build quality, image quality, and optical quality)?. Are there any problems with its plastic body?
I've had limited use of a Composer and Muse. The build quality was acceptable, and I know they've held up well for the owners who use them regularly, though it's a pretty clear step below kit lenses in terms of fit and finish.
I think the amount of enjoyment you get out of a Lensbaby is most directly correlated to the optic you choose and your expectation of it. I've used the Plastic and Single optics and they just don't suit me -- I want tack sharp results and those simply don't do it for me; I find it frustrating trying to tell if something is in focus or wondering if this is just as good as it gets. I don't know how the fisheye optic compares but I would consider the quality of it and what your expectations are.
A different direction: if you want a fisheye for cheap you might also look at the Samyang/Rokinon/Bower 8mm fisheye.
If you are looking for a low cost fisheye, a lensbaby is not the right tool for you. The strong point of the lensbaby is that it can change the focal plane in somewhat the same way as a tilt/shift lens does. That makes it great for artistic shots where you want random focus effects, but not good for extreme wide-angle, as you would expect from a fisheye.
If you are interested in the lensbaby for its intended purpose, the manufacturer is very customer-friendly, and you can look on the lensbaby web site or call them at 1-877-536-7222 (US phone number).
I think if you look at the images in their gallery, you will see that the hallmark of the lensbaby is a sharp focus falloff. Here's an example, so you see what I mean:
As you see, there is a huge wide-angle effect, but more dramatic than that is that the center of focus is so narrowly constrained as to give a somewhat bizarre effect almost like motion to the image.