How can I find out my true legal name?

Here is the lowdown: when I was born my parents weren't married so I took on my mom's last name. But when I was 10-11 I switched my last name to my dad's last name, although they got married but I changed my name before any of the marriage proceedings. I went down to the courthouse to change my legal name back to what it used to be. Now they tell me the total cost is like almost $300 this comes complete with fingerprints, background check, published in the newspaper, and hearing. When I was younger we didn't do any of that, my mom paid like $30 or $40 dollars and that was it. The only thing is my original name change took place before september 11. I live in Michigan so I guess my question is that if my name was legally changed would my parents have had to gone through the same process? my records and everything is under my current name, but the passport agency told me that I can have any name put on records like social security cards and birth certificates. if anyone has experience in this kinda thing let me know.