Unemployment costs $362/week + administrative overhead.
The wage of an auto worker costs from $1200/week to $2920/week (depending on whether you believe the $30/hour number or the $73/hour number floating around).
http://www.michigan.gov/documents/uia/EUC_Fact_Sheet_120_240...
Additionally, auto workers have an incentive to get off unemployment; it pays less than market rate. They have no incentive to stop working for GM, which pays above market rate.