If you're after cheap and just passing, you can replace the pre-cats below the exhaust manifold with regular pipe and either hope the main cat by the oxygen sensor can do the job or get a more effective main cat. I don't think the typical inspector will notice that you don't have pre-cats.

I can't comment on the legality of doing this.

Sixto
95 S420
87 300SDL
83 300SD ... $950, see cars forum
91 300SE ... sold