...does not start anymore

So far, I've only been browsing the forum. But now I have a first problem:
For days, the 3.3TDI has been starting worse and worse. Only after 5sec, then after 7, since this morning not at all. The fuel pressure was measured before the pressure increase pump. He came to 3bar, but he only built up very slowly. As a result, they also tried to start the car with a "direct" sprite, in which the high-pressure pump sucked the fuel from a tank in front of the common rail. The car didn't start here either. The pressure measured at the start (behind the high pressure pump) was only 86bar. Now to the question:
Is the diagnosis, "high pressure pump defective" really necessarily correct? How expensive is such a pump, and what does it cost to use this one and the other? to be expanded (approx.)?

Another question: The car only ran 140,000km. Is there any experience here about culling regulation?

Thank you for your help