If you do the forms, it costs all of $50 at the State of Michigan Corporations Division to file LLC paperwork. There are no discounts but how much cheaper do you want? That said, you perhaps will be "penny wise and pound foolish" if you try to do this 'yourself'. In short: be careful.
Sometimes 'cheapest' leads to problems. You need to have advice about how to make sure the LLC actually protects your personal assets from business obligations, and if you 'do it yourself' you are likely missing issues that may come back to bite you. Similarly, are you sure an LLC is the best option?
I strongly suggest you contact me (or a local attorney to you -- you don't say where in Michigan you are) familiar with business formation, and be sure you're taking all options into account. It may cost $750-1000 to do this right, but it is money well spent to insure there aren't problems down the road! Remember, what you read here isn't 'legal advice' so much as a good 'first stab' at the issue. To provide legal advice we can stand behind, it is important to meet with you to flesh out all the facts of your situation!