Here's a cheaper Sigma 300mm that may work on your cam Carson. This is all I've been shooting lately on my nikon over my VR lens'. It has auto focus but no image stabilization(VR). Kinda noisy auto focus for stealthy shoots but not terribly noticeable from a distance, just enough to make the critters look at the cam and smile.
Best thing about it is it's affordable and is probably pretty close to what you're looking for your lens to do. Just another option for ya.
Has a little macro switch for shooting up close bug mugshots too,lol.
This is where I got mine.
http://www.bhphotovideo.com/c/product/391074-REG/Sigma_508101_70_300mm_f_4_5_6_APO_M_DG.html