Not surprised it's labeled as a "gross polluter". I think all of the Benzs of the late 1980's in So. Cal. are catagorized as such.

There is no way to estimate the repair costs without knowing a bit more info, ie mileage, maintenance history, ect. It could be as simple as a tune up to something $$$$. Per Autotrader, 300e's of that vintage range from $1100 - $6900. If you are mechanically inclined, I say try to fix it for less than $600 and then cut your loses.

If you need help getting it to pass, use the search button.

Best of luck.

Tinker