Here is a data point.

Last week, eBay had an auction of a 1992 300D with 313kmi. See the discussion at

92 300D with Self-Leveling?

It is still active and the price is $4,500 (met the reserve already)

Here is the auction link

http://cgi.ebay.com/ebaymotors/aw-cgi/eBayISAPI.dll?ViewItem&item=599784311