Just a piece of advice. If you do decide to go over to the second-hand car market that gets held during weekends, be very careful. You will find several people who just buy and sell cars pocketing a small profit. This is their business. Many are from car shops that resell second-hand cars. Try looking for a "genuine" seller, someone who is possibly leaving the country. I believe Qatar Living to be good site for such sellers.
Keep a simple rule in mind: Buying a second-hand car is almost always a "blind buy." That is why it is always advisable to buy from a person who is leaving the country, especially from a person who has been a single owner of the car.