Can also consider the Sigma 100-300 F4. In terms of optical quality, this one is on par with the 80-200 and also, relatively fast at F4. And pretty affordable at 1500 or thereabout.
Also, this is a constant length zoom, so that air is not exchanged with the outside as you zoom and focus. As a result, your lens and your sensor would remain clean for a long time to come, if you like to think long term. By long term, I mean a year or two.
With some dust in a 20 element lens like the 50-500, it's gonna to have lots of flare and become very, very soft. BTW, in the first place, it's already soft in the long end brand new as a 10x zoom.