Guys, question, how much effort in terms of man hours does it take to upgrade SCA Elbrus into the most recent version?

Depends on how much is your site is cutomized and how the customizations are done, so there’s not a ‘default’ number of hours to accomplish that

rough estimate if it's just normal skinning

Martin is correct. It could be anywhere between 2 weeks and 2 months for straight-forward customisations, but I don't do them professionally so it's hard for me to say. The gotcha is that because we have moved to the extensibility framework, you will have to reimplement your site's look-and-feel into a theme, which will be significant work

Whenever management asks for an estimate on complex software work I absolutely will not place a number anywhere in my answer. Instead, I ask if they’re willing to invest the time in answering the question responsibly. If they shrug me off, then I know I’ve just avoided a potentially painful project and a ruined relationship. If they ask to learn more then I know I’ve identified someone who might be good to work with.