Vickie, You don't need a torque wrench for anything related to belt changes in a W126 car. A little experience is worthwhile though, to prevent over tightening the belts. A loose belt may squeak but it won't break the bolts that fix the device to its mount (power steering for example, can break the mounting bolts) but this is still not a serious job.
I don't know if you are near San Mateo, if you drop by I will loan you some tools while you work in the back alley, and I will gladly give a few words of wisdom
If you need a good Indy, one that won't overcharge you, I can recommend one nearby also.

Belts for your alternator can be 10 X 1000 or 10X 1037 (dimension in mm's) depending on the year and what the last mechanic had available (there is a lot of overlap in the alternator bracket)
They should run no more than $7 each discount. These are the most important belts on a diesel because they also spin the water pump (read engine lifeline!)
The chances of both belts failing at the same time is quite slim because they wear very slowly so don't get worried and think you have to change these out before next Spring or even next summer depending on how much you drive.

The reason a AAA shop might advise you to change belts is because, unless they are very new, they always show a tiny little wear. Many shops have to say something is in need of repair when in reality it is not urgent. I'll never forget my dad getting incensed when a service station talked grandma into replacing a new belt, they observed it when they checked her oil (yes they used to do that!) They overcharged her grossly, so he actually went down and made them give all the money back after he called them on their scam because the belt was almost new to begin with.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!