If you are talking about the rear subframe bushings, I was in the process of doing mine tonight. It would have been an hour job except that the hole for one of the bolts stripped. Now I am going to have to figure out a way to have it re tapped.
If you dont hit any crazy snags like this you can do it yourself in an hour.
Youll need for a 126 300sd the bushings are part 126 350 01 75 from fastlane for $115
Jackstands ($20) , a jack, a 24mm socket and a 17mm socket, and two screwdrivers to pry out the old bushing.

If you are talking about the front subframe bushings I have the parts on the way. For virtually all the rubber parts in the front it was $208 from fastlane and PepBoys said that they would do all of the labor including an alignment for $260.

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.