I just went through an extensive repair with my '03 4.4i, which included a water pump replacement as part of the overall work being done. The water pump was about $215 for parts. On the overall bill, labor was about the same as parts. So adding in taxes and such, figure a water pump replacement at a repair shop would be around $450 or so. YMMV.

Dave

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2003 4.4i (The X5 is WAAAY more fun than my Jeep used to be... )