Uh, no. I think you misunderstand the situation and the proceedings. First, it wouldn't cost six figures, as I believe Mark is simply retaining this attorney as specialized help. This isn't going to cost six figures. I think Mark will be doing a great deal of the work, but as he mentioned, he may need some help with respect to how family court works, issues about who the judge is, nuances with regards to child support etc.
Second, this isn't a situation where he can counter sue. This is a child support hearing in family court. If he wanted to sue Jan, he'd have to do so in a separate action.
It's nice to have some smart attorneys on the boards