You won't find anything less expensive.
I have NO idea if my dad is my biological dad. There have always been suspicions by me, and this unsaid tension in the air. I look nothing like anyone in my family ever. I don't have any of the hereditary stuff, or the mental health issues. I am blonde, fair, green eyed and tiny. Every person in my family as far back as we can trace has dark hair, dark skin, tall and large. In fact inside side of me, I know he's probably not. There were things happening in their lives when I was conceived, I don't think he was even THERE to get my mom pregnant.
My life is NOT a lie. I know who my dad is. He raised me. He protected me. He played with me. He loved me. he laughed with me. He brushed my hair. He read to me. He held me when I cried. He was there for me. I have not even explored who my bio dad could be. Why? Because, he isn't there for a reason. I could look for him and find him and guess what? He probably has this whole life that didn't have anything to do with me. A family. I would not be welcome, I'm sure. I would be something that would drop an A bomb into his entire life, and it would not be a happy meeting.
When people "lie" in situations like this, like I think my parents did...it's usually for the very best. There is usually a very real reason, and you would find that out if you went digging. And, you probably wouldn't like what you find.
You think you need to know, but really I don't think you do. There is no closure to be found, I'm afraid. Why do you think you need to know by DNA? Your life isn't a lie. Whoever raised you and loved you was your parent. What are you trying to prove? How will it even help or better your life?