A cheap alternative to long lenses over 500mm are mirror lenses. Cost effective, light, and extremely portable, mirror lenses have become popular with amature photographers who operate on a tight budget. One drawback of mirror lenses are the unusual bokeh or blurry circles.
|Sigma 200-500mm f/2.8||$26,000|
|Tamron 200-500mm f/5-6.3||$1000|
|Vivitar 650-1300mm f/8||$230|
|Pro Optic 500mm f/6.3||$160|
A typical lens provides a smooth bokeh, usually a solid round circle. Bokeh from mirror lenses provide a hollow circle, almost like a doughnut. Compare the two images below. Notice the top image has smooth colored circles while the botom image has a large group of "doughnuts."