That depends on where you live, the trim level of your vehicle and its condition as well. Because I don't know all of this, I can only give you an idea based on Kelley Blue Book's results.
The suggested retail value of a 2006 Monte Carlo LS Coupe 2 Door with 2000 miles in excellent condition is worth: $18,015
Remember that trade in values are usually lower and private party values are usually higher. Try playing with the tool on www.kbb.com and see if you can get it to be more accurate for you.