Good news. Car passed smog test after replacement Cat was installed.
Price of new aftermarket Cat, installed= $350.00
Cost of labor and diag = $50.00

I was lucky and new one from Benz Shop would have cost me $700
I am going to use Rahulio1989300E's guide to replace my O2 Senor come next pay day.. Thanks for posting it Rahulio... thanks all for your help..