It's usually not the "shocks" (which aren't--they're levelers) but instead the accumulators (which are the shocks).

The accumulators are round pressure vessels hidden under the rear floor. They're more like $100.

Since the levelers are indeed VERY expensive, they are only replaced when leaking/broken and not necessarily in pairs.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles