What is the usual cost to replace the 2 front lower control arms (forward)?

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I brought in my 2010 BMW 328i to check the alignment, as it drifts slightly left. Mechanic said front lower control arms (forward) bushings are cracked and causing arm to shift, and should be replaced before fixing the alignment. My car has 55,000 miles. Is this a typical, maintenance repair? What is the usual cost for such a repair?