The 2 cheaper 50's - one's a "G" and one's a "D"
Arguably, image quality is better on the $200 (G) one vs. the $100 one (D).
The $400 one vs the $200 one- max aperture is 1.4 vs 1.8, probably faster & quieter AF, and probably better glass.
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Internet comment - take it for what it's...