2003 Audi A4 think its a catalytic converter problem

Yesterday when I started my car after work, a warning light came on that according to the manual is a malfunction light. On the 7 minute drive home, the car shuddered to the point I thought it would stall at any minute. The light flashed continually and the manual indicates that that may be the catalytic converter. If this is the issue, what should I expect the cost to be around to rectify?