@ Peter, I found this on the AM forum !
..These are very expensive cars to service. I just did a tune-up on one..plugs, coils, airfilters, fuel filter, and front brake pads only..parts alone 6k. Add the labor. Intake manifold must come off to service the sparkplugs. Intake gasket alone was 400 bucks. Nice car though..glad I don't own it.

Here are the Porsche service prices.
EUR 219,00
964 C2
Service Prijs
Classic prijs
Onderhoud 1990 '91
20.000 km
EUR 1.539,00
EUR 1.239,00
Onderhoud 1992 '93 '94
20.000 km
EUR 1.459,00
EUR 1.179,00
Groot onderhoud
40.000 km
EUR 1.659,00
EUR 1.339,00
Groot onderhoud
40.000 km
EUR 1.679,00
EUR 1.349,00
Groot onderhoud 1990 '91
80.000 km
EUR 1.709,00
EUR 1.379,00
Groot onderhoud 1992 '93 '94
80.000 km
EUR 1.749,00
EUR 1.409,00
Remvloeistof (i.c.m. onderhoud) '90 - '94
EUR 189,00