Have XM Roady 2 mounted on top of dash - to the left and at back of storage tray. Easy install. Used Pro-fit mount(from my Jeep Liberty) and bent to fit contours of dash.Then used existing screws with one additional screw added for stability. Very clean look and sits up so I can see while driving. Does not block view and with orange display comes close to matching Xterra's dash lights. I have non-RF HU so used fm modulator to connect directly to antenna. Everything stored very easily behind HU. Not a hard install but watch out for scratches.

Based on your post - you have Xterra SE which comes with RF stereo. The $400 is for tuner (tuner is mounted on drivers side kick plate under dash) with glass mounted antenna. Will allow control from steering wheel - I believe. Very clean but also somewhat expensive. I have seen Roady 2's for 49.99 recently and with FM modulator you could install for about $100 - if DYI.