looking for an >400mm third party lens

[xps]

My Canon 300mm 2.8 II is heavily broken, a NACA 7. I used it with the 1.4 & 2.0 converter
Now I am looking for an new lens >400mm.

As I looked in the www, the Canon lenses are extraordinary expensive. Does anybody own an >400mm third party (Sigma, Tamron, Tokina,...) lens that is worth buying? I do not want to spend another 8000 € for this lens....

 

[Loswr]

Do you require autofocus? If not, older Minolta supertele lenses (500mm and 600mm) come up on eBay, etc., from time to time, and are not too expensive (relatively, that is).

 

[xps]

Do you require autofocus? If not, older Minolta supertele lenses (500mm and 600mm) come up on eBay, etc., from time to time, and are not too expensive (relatively, that is).

Yes, AF is required. Using 60D, 5D2 (and maybe in some month the 7D2
Seen the Sigma 800mm. Is this lens ok?