I'm thinking of surprising my wife with an assassin
That's a serious issue. Why would you bring an assassin to surprise your wife?
I would bring an assassin to punish my wife.
You are angry at your wife and want her to be punished, but this is so very over the top. Surprising people is good if it is a happy one and not a frightening surprise. Your wife will be so scared she will die of fright alone.
Maybe she will learn to stop spending so much money after this.
This is not the way to surprise anyone. If you want your wife to stop spending money more than necessary, you should sit and have a conversation with her. It's unnecessary to threaten her with an assassin.