It is unusual for the oil pump to go. I would try to verify that it really is a pressure problem. These cars have an electrical transducer to convert oil pressure to a proportional voltage output. You can replace the transducer. Mine cost $57 (part only). If you are mechanically inclined and can get ahold of a mechanical oil pressure gauge, then put a fitting where the transducer is and verify the pressure with the mechanical gauge. Otherwise have a shop verify it.

Meanwhile, while driving the car, don't let the pressure get below .5 to .7 bar. I kept one foot on the brake and one on the throttle and always added enough gas to keep the oil pressure up. I drove like this for about 6 months before the timing chain broke and I was forced to take everything apart. (the two were not related, the chain had 218k miles on it)

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)