I had a 96 318ti. I guess I will just come out and say, don't buy it. Parts really are outrageously priced. You can quickly spend a lot on the simplest of things. They are also not really
that slow, it just looks bad on paper (138hp/ 2,800lb dry weight) it still has enough ooomph to spin the rears.
Common problems, and problems that I had with my car within 6 months: Radiators go bad freuquently, persistent vacuum leaks, leaking rear shocks, hatch strut supports more than likely are bad, the M42/44 engines are known for bad oil leaks (mainly the rear seal.), alternators,and the power steering likes to go. Electrical problems abound. There is also a little plastic piece that likes to break. It holds the window actuator arms in the tracks on the window. If it breaks, you will be replacing the plastic piece, the actuator, and the motor in the window ($250 new total).
If the car has ANY motor problems (tapping valves, smoking, other noises), or transmission noises, walk away. You could easily spend 2 grand rebuilding it. The syncros for 2nd to 4th on my car had gone, and I was quoted $1500 for a rebuild! If the alternator goes that's $350 (for a brand new one). I wouldn't worry about interior problems, a trip to a junkyard/pull a part can fix any of that.
On the bright side of things, real world MPG for me was 27 highway/25 city with a heavy foot

and 32 highway/27 city with a light foot. On a trip to Myrtle Beach one time, I even hit 35 MPG cruising there and back.