So it looks like your smoker is ~2.5 years old. The 3D WiFi is $1035. The 3D isn't on the site right now, but the wi-fi appears to be about $150 more, so let's say the 3D is $900 new. I don't even know if warranty is transferable, but the warranty on the auber is expired and the warranty on the box is as good as gone so it's effectively out of warranty. A 2D WiFi is $835. Unless there is something exceptional about the cover I wouldn't give it any actual value.
So... I would suggest a starting price of $650 and be prepared to go as low as $500 depending on your market and how badly you want to move it. I'm just basing this on my own valuation and what I would consider paying for it if I were in the market. Hopefully you'll get some more responses to help guide you.