Tokina 400 5.6 AT-X, somewhat slow, but sharp, I have one in Minolta Sony A, I know they were offered in Nikon and Canon Mount, I paid around $100 for mine. Sigma also made a 400 5.6 that runs around the same price. Other option is MF 400 third party lens, rebranded Soligar, Star, and others, I dont recall who make it, sharp but contrast suffers as it only single coated. Most are 2 elements in 2 groups. I have a Soligar 450 F 8 version in M 42 that I use on Sony E with adaptor, Pentax K5 with K mount adaptor and Sigma SA with 42mm adaptor. There were also 500mm made as well, but seems to be softer than the 400mm. I would not pay more than $50.00 for any version. Last option is MF Vivitar 600 reflex, S1 F8, under your price point, don't know how well it will do with a sensor. Any sins are in the corners that will not show on a cropped sensor.