How do I find my real biological dad for free of little money?

Then start Googling and making phone calls, and visit if the place is close and within your budget.

You need to talk to your mother, her siblings, and any classmates from that time period if she was in school when you were conceived, or coworkers if she was working. Talk to your grandparents if they are still alive.

You are looking for pictures. You are looking for someone who knew him.

Be aware that you may not like what you find. He could be dead or in jail. He might not want to be found, and might reject you.