I found this site for you
anyone can do a name change. In theory, most states allow you to legally change your name by usage only -- meaning that you simply start using your new name without any court action, and at no cost.
However, practically speaking, because you don't have a marriage certificate, you will need an official court order changing your name before you'll get government agencies and many private companies, such as banks and title companies, to accept your new name.
When my bf got his done last yr it cost 200 dollars
For e it cost $200as well.