Volvo V70 Bifuel – replacement of the gas distributor

Dear people, for some time now the car has been running out of gas. Driving is then only possible for a certain time on petrol operation. Then it goes back a few weeks and the error comes up again. Today the Volvo was then with the friendly one. Then the hammer: it would have to be replaced the gas distributor, spark plugs and filter. Cost point:1.500 Euro!!! Edit: How is the error in the gas system actually determined? Or would not the system have to be adjusted first? Can someone give me an assessment whether the price fits and maybe someone else has had such a mistake? Thank you for your feedback. Greeting odddo