There really is no "average" fee. Michigan law entitles the PR to "reasonable compensation" for their services. It does not define what reasonable is. In my experience, the courts have looked at factors like: 1) the normal compensation of the PR (opportunity cost); 2) the complexity of the estate; 3) the size of the estate; 4) the time required to perform the services. There are sometimes other factors as well.
I would argue that, except in cases where the Will expressly provides it, or in cases where the estate is extremely large, that charging on a percentage basis is a recipe for problems. The PR should keep a journal of his or her services and keep track of the time spent. He or she then needs to determine a reasonable hourly rate for those services, based on the above factors. If anyone objects, the probate court can determine if the compensation is reasonable.
There is no set fee or set schedule of fees in Michigan. The fee must be "reasonable." All beneficiaries are entitled to an accounting, including an explanation of personal representative ("executor") fees.
According to MCL 700.3719:
"(1) A personal representative is entitled to reasonable compensation for services performed. A personal represntative may pay the personal representative's own compensation periodically as earned without prior court approval.
(2) If an attorney serves as personal representative, the attorney shall maintain time records that state the identity of the person performing personal representative services, the date the services are performed, the amount of time expended in performing the services, and a brief description of the services. Upon request of an interested person affected by payment of personal representative fees, the attorney shall send the time records to the interested person."
Hope this helps!