Replace rear wheel hub assy with speed sensor

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I always feel as if I'm being ripped off by the dealer!!! 3 warning lights came on when I started my car 1) Service traction 2)Service ABS 3) Service steering - not the exact wording!! When I took it to the dealer they said I needed to replace my left rear wheel assy. with speed sensor. Total repair bill $774 including taxes. Was I ripped off???