My children are using their stepfather's last name in school. I want to legally change it. I have read here that you need consent from both parents but I I can't find their biological father. I know that he is not using his legal name because he is in the US illegally. I can't get chld support for the same reason. I can't afford to have my husband adopt the kids we just don't have the kind of money needed. What are some options that I have?

... I can't afford to have my husband adopt the kids we just don't have the kind of money needed ...

Why do you suppose a name change would cost less than an adoption?