Anything along the Lake Michigan lakeshore should be open, from Warren Dunes to Sleeping Bear Nat'l Lakeshore. The big lake helps keep the shoreline warmer in the fall so the colors change a bit later than further inland.
Check out Charles Mears State Park in Pentwater. The park is very close to the lake. It's just south of Ludington. We usually stay at Van Buren SP near South Haven.
It depends upon what you like to do because beach life is pretty slow at that time of the year unless you hit a warm spell.