I have had a quick look, as it piqued my interest, and the part appears to be shared with the Prius of the same era. Consequently, it is available in plentiful numbers and quite cheap (under £50) second hand.
From what I can find online, the part is 89680 in the image, which appears to show it is located in the rear on the passenger side. Depending on what needs stripping out to get to it, the rock and roll bed might have to be removed, but other than that it looks like a simple swap. I can't see why it would be nearly £1500, but there might be an explanation.