Sigma and Tonkia made 400 5.6 that are inexpensive, I have the Tonkia, maybe not the sharpest 400 ever made but well enough on my Sony's. I also have a Sigma safari green that only works on my film Minolta 9000 in AF mode, but works well enough manual focus with my Sonys . In 600, the only lens in my price range is the Sigma non AF 600 F8, a pain to use as it is close focus and has a long reach a lot of travel when focusing.