my opinions:
1- Penfed is not a good credit union suggestion, nor is it a good one to just "join." Their lending standards in some cases are stricter then some large banks. Reconsider just joining them until you do some research.
2- john's statement is correct. but as you have said some people just do not want/do not have the ability to deal with the hassle of detailing the car, publishing the info, making appointments having people no show, be late, taking risk of robbery/theft, dealing with promised payments, sale paperwork, and then the intrinsic difficulties of selling a car with a lien on it. Then dealing with any issues 6 weeks after the sale if th engine goes, or the brakes have an issue or if they want to give the car back to you since they lost their job. (all of that is first hand accounts I have heard from people) To some it is a lot easier and worth it to just go to a dealership and turn the car in and write the loss of as a cost of doing business.
I myself do not have time with my work schedule to deal with trying to sell a car mysel if I was in that circumstance
if you ever read the book "Freakenomics" there is a chapter dealing with if your real estate agent is trying to get you the best possible deal or not. In reality, its the best deal, just not the best possible, a RA would push you to take a deal just to get it done, so they could move on to the next client- and a $10,000 diference really effects their commision not that much, whereas if they were selling their house they would hold out for that extra $10,000.
3- taking negative equity into a used car transaction makes things more difficult. You will need to have a strong downpayment to help secure financing and ensure a better rate.
4- Since you have 5 months, you need to view your car choice as an endurance runner would view an upcoming race. Ramen noodle it, (ie: lower your quality of life/expenses to give you the best amount of money to put into the transaction) and do a lot more research.
Figure if your bank will give you financing, start looking for a car, you may even be able to find deals (going into summer maybe on something small like a new Ford Focus that you could buy with a good apr/rebate set and give youself a new car warranty vehicle). Consider eligibility for a credit union.
