Sorry but if he is not going to "just sign the papers" it is not going to be cheap, and it will never be free ( you will have court costs at the least)
So if he is going to fight over custody of the child, the cost will go up fast.
If he will agree to all the terms of separation, custody and the such, then you can do it cheaper.
The best way is to have a local attorney write up the paper work, and send it to him to sign,
You can order the paper work online ( but don't get any legal advice)
There should be a legal aid in your area, If you can't find it any other way check with your local social service agency they will have referals for legal help normally