The first attorney answered your 8th amendment question, but there are generally a couple of other questions buried in that type of question. One, if you're on probation, you can't be found guilty of violating your probation for failing to pay restitution unless it can be proven that you are WILLFULLY not paying. Two, if you and the other co-defendants are ordered to pay it joint and several, any ONE of you can be stuck with the entire bill and it will be up to you to sue each other over the differences.
You've posed an excellent question. If the order was a fine, then you may have a good argument that a fine amount set so far above the ability to pay is an excessive fine under the 8th Amendment. However, restitution is not considered a "fine" for purposes of analysis under the 8th Amendment because it is not punishment - it is being used to compensate the victim for actual losses. So good idea, but it won't work.
However, you should consult your attorney, or if you do not have access to one then your probation officer, about modifying the payment terms of the restitution order so that you can make payments. Judges and probation officers are generally understanding when you genuinely cannot pay.
Good luck to you.
Unfortunately, you will not get any relief by argument the 8th Amendment. That's a good, creative idea. However, you will probably get relief if the probation officer wants to put you in jail or otherwise have you sanctioned for getting behind or missing restitution payments. What I mean is that your ability to pay measured against your efforts to pay is the analysis that a judge in Michigan is required to do in the eyes of the law. Good luck.