The easiest way to estimate these jobs is to look up the parts on Fastlane.
Center Tie Rod ~$80
Left Tie Rod ~$60
Right Tie Rod ~$60
Idler Arm Repair Kit ~$30
I believe he was referring to the Guide Rod Mounts (aka thrust bushings),as they are a common wear point on the W126 front end.
Guide Rod Mounts (2)~$180
As you can see, the parts price isn't that far off. Depending on his shop rate, 3-4 hrs labor is pretty darn good. Is he including an alignment?
If you do it yourself, you are basically looking at saving only the labor cost. So the only factor is spending the money vs. learning how to do the task yourself. About the only "special" tool you may want is the tie rod tool.
http://www.zdmak.com/wbstore/main.asp?action=PROD&PROD=MK-1954GT&CTMP=1