I don't know about the Detroit area but I think it ended up being around 3-4k for a 2800 sq ft ranch. My house is brick so it had to be done from the inside. They drilled two holes between every stud (one at about 6 ft and one about 3 ft), filled it with insulation and then put the plug they created with a hole saw back in. They used a lot of plastic sheeting around the house to limit dust and had a cleaning person follow them in to clean any messes they made.
If you have siding, they can do it from the outside and will probably be less than if they have to do it from the inside.
We noticed a huge difference right away in terms of comfort and a noticeable reduction of noise from the outside.