If it looks reasonable, drives OK, and doesn't need any major repairs I was thinking $3K, perhaps $3.5K. Compare it to this car:
http://www.peachparts.com/shopforum/mercedes-cars-sale/339656-fs-1993-w124-300e-2-8-phoenix-az-area.html assuming it will sell for a few hundred less than that asking price.
I'd like to see some more info based on what the previous poster has stated wrt value. His numbers are almost exactly what I paid for my 1993 300E 2.8 with 80K miles - when I bought it in 2003. You can buy the best 210 E320 out there or even a 211 car for that kind of money. I wouldn't pay that for a daily driver 124 sedan or wagon.