His asking price doesn't sound unrealistic, if the condition of everything is indeed "excellent to mint" as he states. 573 manual focus + 291 auto-focus cameras... 864 in total, at a pessimistic $50 per camera is $43,200. Then there's 573 manual-focus and 337 AF lenses... many of them could be very basic, but possibly some nice pieces... 910 lenses in total at $30 per lens is another $27,300. We're already up to nearly $70k in total.
The problem is, who - other than a big dealer running low on used vintage stock (and how many of those are there?) - is going to buy everything in one lot?