Aside from the model preference, you should also consider the engines it comes with. earlier M54 engines are solid and bullet proof. They are in the e46. then in the e90, they moved to n52 & n53 engines, with the latter on 325i. So far, the rod bearing issues are more on the n54 & n55 engines, but not n52 & n53. Again, these are wear n tear items, so at certain mileage, you would still need to change it. if the car has been taken care off diligently, such issue rarely occurs. injectors, it will have to be serviced, as its already aged quire sometime.
Initial preventive maintenance could go upwards to RM10k. COULD.... as it depends on the condition of the car, how well it was maintained. some are truly buy n drive, while some are a 'work-in-progress'. Again, if possible, do find a unit with full service history, so at least u wont have that much of a headache, and u can plan you maintenance program.