DTW-CHI is as low as $139, same day return.
It's either that or start the trip as a Base member. It will take 1-3 days for the mileage to post and then at least another day for the status to update. Then you usually have to remove/add your WP # in the record.
And then sometimes it still doesn't work. For my first upgrade (occurred while we were flying ATL-AMS) after our return to ATL we had to ask the gate agent to verify our status & manually force us into the upgrade list.