First, remember a car is NOT an investment. You WON'T get back all the money you put into it. Not even close. You paid to drive it while you had it :(
Is there a CarMax near you? I had success selling my car to them before I moved cross country. It's basically like doing a dealer trade in, but they don't require you to buy a car from them for them to buy your car (they don't even ask... it's a whole separate thing). In general you get a LITTLE more than the trade in value, but LESS than the private value.
The nice part is, they handle all the paperwork, so you KNOW the loan is taken care of and title documents are fine.
The quote is good for 7 days, so take the car in, get an offer from them and then decide if it's worth it to you. I got my offer and then went back 5 days later and had a check in my hand in 30 minutes. They paid me $15500. I could have gotten $18000 on my own, but it would have taken a LOT more than 30 minutes, and I would have had to deal with the hassles of money transfers, paying the loan, transferring title etc. I owed 10k, so walked away with 5.5.