Excellon is Kenwoods better model line. They are nice, but just curious about why you want this specific one. I didn't search Kenwoods site, but it doesn't look like this one has navigation, or any video screen. It looks like its a double din touch screen. You can get all these features and more in a single din for $100. Most of the single dins will have a front side USB input. Just to make sure, this is an audio input device. This will not allow you to add an amplifier. What other audio input source are you trying to add? If you do add any amplifier to your factory head unit, you will not have the function "time alignment". Which means any speakers coming through your amplifier could be slightly delayed throwing off the sound.
MY OPINION HERE, (so feel free to blow this off): I don't like the 7" touch screens. The 6.2"-6" double dins will have a few buttons on or knobs on the side to make it easier to do some of the basics like change track/station or change the volume easier by feel, so you don't hit the wrong button on a touch screen or need to divert your eyes to find it. Not sure if you have steering wheel controls or not. Was there any specific function or reason for this specific model? Not trying to change your mind, just throwing out some questions that might help get you where you want to go.
Heres a few I can think of off the top of my head. Most will have weekly deals, specials, clearance, open box (returned may or may not be new). Not sure how flexible you are on which one you want.
Crutchfield.com
woofersetc.com
parts-express.com
pacificstereo.com
techronics.com
Also for electronics
Frys.com ( I have found stuff here that was out of stock/discontinued EVERYWHERE ELSE before). They also have some good weekly and daily deals if you share with them your email.