For the $5000 limit on the amount that you are specifying, you will be getting some extremely high mileage cars. Most of these cars will have been well used, especially the BMW, Merc, Audi and Lexus.
Even if you can get a decent Merc or BMW, Audi or Lexus, you MUST remember, there is no such thing as a cheap Merc or BMW or Audi or Lexus. Not only will these cars require a lot of maintainance, because of their age but in some cases, it may eventually become more than the car is worth.
Choose carefully, yes the Merc and BMW are wonderful cars and a pleasure to drive, but out of your list these two may be the only cars that will still survive after a some time and still give you some change back if you decide to sell.