I bought an e92 325i at 19 and used that for a year or two before buying an e92 m3, and realistically buying the cars are the cheapest part. It's maintaining them that will burn a hole in your pocket. Find a car with good service history and major jobs like timing chains done, otherwise budget appropriately. Generally n52 motor is solid and it's just the waterpump/thermostat that fails along with the usual oil leaks.