I have a 6 month old daughter her father wanted her to have his last name so I gave my baby his last name but needless to say he is not even apart of her life anymore I live in west Virginia and he lives in ny my question is how much would it cost to change her last name

Ask an atty in your local area, he/she should be able to give you the cost if it's do'able, father probably has to consent.

You can use any name you want as long as thre is no intent to defraud. Just start using your last name. If you to do it formally go to Family Court and file a petition.