Here in the forum at Fastlane, they offer the fuel filter for you 1994 E320 for $20-$25.
Regarding the labor it should take no more than 30 minutes according this:
http://skinnerbox.steaky.org/Service/W124/w124CD1/Program/Engine/104/07.3-5563.pdf
Total cost in my opinion looks like it should have been more like $60.