I see all kinds on ebay, all price ranges. The only number I could find on mine was 176 911 023 547 Bosch. Are there more than one starter that will work?
Any diesel starter from a mk1 (sometimes) up to the mk3 ones will work. Mk3 ones require a bit of wiring IIRC. You can only use one from a mk1 if it has the same or more bolt holes then the one that is currently on there.