2001 Volkswagen Golf Blowing black smoke

We don't get involved with costs here because there's way too many variables. We don't even know what's wrong yet. What have you checked so far? Are there any other symptoms or observations? With no other clues to go on, the place to start is by having the diagnostic fault codes read and recorded. Those will indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. The people at many auto parts stores will read those codes for you for free.