According to The Economist, which invented the Big Mac Index, it was never intended to be a serious economic indicator, but it has become a common measure of purchasing power.
The following links are specific to Michigan.
Comerica Bank Michigan Indexes and Outlooks
RSQE Forecast--University of Michigan
Federal Reserve Bank of Chicago/Detroit Branch -- Michigan Economy Blog
Guide to Economic Indicators by 
The Secrets of Economic Indicators by 
The Trader's Guide to Key Economic Indicators by