If I remember correctly the 501CM also has the gliding mirror system (which is only useful with long lenses, like 180mm and up - do you plan to use those?)
$2k seems a lot, unless the thing is really like new, has an acute matte D screen, a new type A12N (with dark slide holder), etc.
Not sure how the 80 CB compares to the others... some CB lenses are identical to the CF/CFi, not sure about the 80mm.
As Toasty said 2 posts above, Hassy pricing is all over the map and this $2k 501CM is just another example of it...
Good luck with your search! (it’s also part of the fun)