Sometimes a telephoto lens is useful in nature photography. But when it comes to costs everything beyond 200mm or so can become very expensive. I found out that it depends on two letters: AF and IS. There is not much choice especially if you need a stabilizer.
So, some years ago, I purchased a Novoflex follow-focus lens, with a 400mm and 600mm head and a 2x original Novoflex converter. It cost me around 500$ and looks like a lens that had really been used by a professional.
That beast is heavy, aperture starts at 5.6 at 400mm, 8.0 at 600mm. Right, you can choose between a good tripod and high ISO film. The image quality is amazing for a lens that old and that cheap. When it comes to the converter the image quality is not that good but probably still good enough for a 10MP camera, provided you set the camera and lens in concrete - 1200mm focal length at f16 is a combination that dislikes even a moderate breeze. In fact, I use that set with two heavy tripods for landscapes.
Now you can see why I ask this question:
What are the alternatives if you want to shoot with ultra-long telephoto lenses and your budget is limited? Are there catadioptric lenses longer than 600mm? What about telescopes?
