Wife Was Paid

I had an old buddy come over that we hadn't seen in a couple of years. We'd had a threesome once several years ago when we were all drunk and we were drinking pretty heavy this time, but my wife outgrew that easy drunk stage.
He made a few jokes about it and we knew he was seeing if she was willing, and I made the joke that I'd go along with it for a hundred bucks.
It pissed my wife off, sort of, but I dared her and she couldn't pass it up.
He put a hundred on the table and she picked it up and took him to the spare bedroom for an hour, sneering at me as she waved it between us. I really didn't mind, lol, I think she deserves some strange once in awhile and she knows it.

The thing is, afterward, she liked doing it for money and she wants to know if she can do it again for real, with a stranger for more.

How do I even go about that?