I now use only a D500. Lenses I use are:

300 PF with 1.4
Tamron 150-600 G2

I use the 300 when I don't think I'll need a zoom and when I want to go light - and - the light is less than ideal.
I use the Tamron when I think I'll need a zoom and the light is good. If I have bad light and need a zoom I'm not well setup... Maybe should look into the Tamron 50-200 for such times (2.8) as well.

I used to do different kinds of photography but now it's only birds...

So, I can get a Nikon 500 f4 APS non-VR - for $2800. It's in very nice shape.

My thought is this could be used with good or less than ideal light - when - I don't need to be/want to be mobile (which I use the above two lens for).

Do you think this is a good purchase given the above info?

In terms of shooting styles - I have mostly been an on the go, handheld shooter... but I think I should also work on my less mobile, find the right spot and wait for your shots kind of approach as well. Hence the thoughts on this lens. I can afford it - but it wouldn't usually be my first lens for use (most days) I'd think. I have a good enough tripod for this already but would be purchasing a limberly rig for use with it.

Even if I don't use it that much - the price makes me think renting instead is not a good option as only renting 4-5 times would pay for it. I'm 52 and fairly fit (can run around with the tamron - yes it's much lighter) - all day without a thought.

Thanks for input.