Our biggest one time loss to these guys has been about $25K in C/Bs. They also have gotten into buildings and pulled out all the feeders on us overnight (Which is faster than they were put in, to be sure).
All the breaker houses I know of are on the lookout for this type of stuff, so I don't know where they "fence" them. (Derelicts don't generally "find" new 65K breakers in trash cans).
The losses can be covered by insurance, but the time lost obtaining new replacements has absolutely screwed us on finish dates, and even though our suppliers have jumped through hoops to get us new ones, jobs have gone into liquidated damages status because of them.
Wish I'd have known that one was in UCI, I would've liked to have gone over and kicked him.