Learned something interesting the other day that doesn't appear to be in the wiki.

I suppose if someone wanted to add it, it should be under the entry regarding parties and adding another player to your tab.

If two players both add another to their tab, they will split the cost.

I tabbed a friend yesterday and another friend did as well and it only charged us 5 energy each for her elevator cost.
It's a bit confusing though because I couldn't find any indication that we'd both done it (like the indicators showing that someone is tabbed by you or another person, but no indicator for both.) We figured it out after the fact when I asked if someone else had tabbed her as well because it had only used 5 energy.