blk2004rx8

Good Morning, I have a 2004 Mazda RX8 Automatic with roughly 46,000 miles on her. And I just got a CEL and the code was P0037. I know its the rear bank 1 sensor 2 sensor. However does anyone have a picture of where it is on the car and is it easy to install? Also does anyone have any idea of where I can get one from and where it will be the cheapest.

Thanks so much for all of your help