Last time I checked it was about $380 to $450 each for the rear bumper and the rear door panel from St. Charles Isuzu. You might try them on current pricing, but they usually give a percent discount as well as free shipping.

http://isuzu.stcharlesauto.com/parts...rts_department

I actually just got mine replaced from a car wreck, but the body shop got them from a distributor or somthing.