Depends if it is the chrome or rubber bumper model (they swapped over in 1974). Rubber bumper models are worth around 40% less than chrome bumper cars and convertibles are usually worth a bit more than coupés. Prices below are for the UK. If your in another country I'm afraid your guess is as good as mine.
Condition 1:£3600-£8750 Immaculate
Condition 2:£1400-£4500 Reasonable condition
Condition 3:£500-£2000 Piece of ****