The last time one of those 13mm F5.6 sold it only went for US$19,000 on ebay auction. Could it be the same one?... someone could be trying to make a quick profit!
A couple of years ago I saw one of these: http://www.mir.com.my/rb/photography...yes/6mmf28.htm on Ebay and they wanted US$45,000 for it, they kept re-listing it a few times and I think they reduced it to US$39,000 but I don't think it ever sold.
That Sigma 200-500mm F2.8 is just silly what were they thinking when they designed that atrocity? So what if it is F2.8 and has a zoom? I can't really see a justification for its existence? I'd rather loose a couple of stops and use ISO25600 and just cop the noise rather than lug that thing around!