You should only need to go to the County Clerk (thats what I did) to get a Fictitious Business name statment. That cost maybe $15. Then you have to have it publised in a newspaper to show the community that you have the name. I did that in a a major newspaper down here and I think it was $40. They also sent a clipping of the publication to the County Clerk or whoever. If you dont do that, you will get a ton of offers in the mail to publish the name in cheaper newspapers, but you would probably have to send in a clipping of the print your self.
Ok, then you have to get a business license. Head on down to where ever you can do that. I forgot the name of it now, but the building probaby has your city name in it For my city, it was like $25 for the first 6 months.
That should be everything if its just you doing the business. If you have employees, then there will be a lot more work