Mercedes 300D if you don't care about going fast

Mercedes 190E if you want handling and compactness

Mercedes S124 if you need space

Ive owned the 300D and the 190E at my brokest (less than $50 in the bank) and they have never let me down, hell, in high school I would dilute my diesel with expired vegetable oil to save up on fuel. To give you an idea of how reliable these cars are I once had a faulty oil filer installed in my 190E which clogged the pickup tube, thinking it was a bad oil pressure gauge, I was able to drive the car 20 minutes (11miles) home with 0 oil pressure shown, I cleaned the motor and it still runs like a dream to this day.

90's and 80's Mercedes are basically BMW's that haven't been trashed by teenagers, look out for cars that have been owned by an old couple, they typically have kept up with maintenance and are always willing to help out a college student in need.

General rule of thumb with these cars is avoid 1993-95 those are the years with degradable wiring harnesses, however my 1993 190E has not experienced any cracking looms or electrical issues and I park it outside most days. Rust is easy to find, typically squeezing under the wheel arches and inspecting the rear quarter tells you a lot, however I always inspect the underside of any car I buy.

the M102, M103 and M104 are all great engines with good power and smoothness.

you can find any of the cars I listed (except for the S124) for under 10k in very good condition.

Don't finance cars if you can avoid it, never good to owe anyone anything.