my advice. Sigma 50-500 will be best suited for you. u get all the range you want. and with HSM, u will be able to focus fast enough on ur camera body.
i will definately NOT recommend a amateur to get a 500mm prime. since it will cost 10k over.
tokina has a 300 f/2.8. sigma and tamron has them too. Tamron has a SP 300mm f/2.8 however the lens is a MF lens, Sigma has a 300mm f/2.8 HSm, but i havent seen anyone using it.. Tokina 300 f/2.8 ATX-pro lens, 2nd cheap too. but wouldnt recommend unless you really wish to buy a lens to keep and collect dust.
Nikon lenses / Canon lenses primes are super pocket killers for amatuers, but the image quality the give command the price.
if you want range, u can consider the following lenses.
a) Nikon AF-S 300mm ED IF F/4 + 1.4xTC/ 1.7xTC (u will still able to AF fast enough since its AFS)
b) Nikon AF 300 F/4 ED IF F/4 +1.4TC (slow af due to stacking, but still managable)
c) Sigma 100-300 F/4 HSM + 1.4xTC/ 2X TC (you will maybe lose AF if u stack 2X, Image becomes extremely soft when you stack TC)
d) Sigma 70-200 f/2.8 +1.4xTC/ 2XTC (functions as a 140-400mm f/5.6 lens, still can AF, but hunts in low light conditions, same problems with some sigma lenses, when stacked, gives soft image)
e) Sigma 50-500mm - good lens, all rounder. but cannot stack TC, its possible to stack, but u will definately use AF.
e) Tokina ATX-PRO 300mm F/2.8 +1.4x or 2X TC, still fuctions, but i dun see a point why.. image very poor. colour contrast too.. AF Slow like molasses.. dun even mention stacking with a TC.
Sub 2K SUper telelens.... Sigma 50-500... 2nd hand 1.4 - 1.6k or even lesser. my bid goes for 50-500.
