[csapp05]

Good lord people!
The VW TDI common rail diesels have millions of miles of service world wide, like the one poster said the HPFP is like a one percent failure rate. 99% have no HPFP problems.
The system works like this, an in tank electric fuel pump pushes fuel to an electric fuel pump which supplies the approx 80psi fuel to the cam belt driven High Pressure Fuel Pump that then ups the pressure to over 25,000 psi. It feeds a common rail that feeds 4 injectors.
The expensive bill is due to all components which have diesel flow thru them have to be replaced! You have to drop/replace the fuel tank, blow out the lines, replace all fuel pumps, open the timing cover and lock down timing, replace and time the HPFP, all fuel lines and injectors, fuel filter and I am sure forgetting some things! Not for the faint of heart!
Why? VW says since the system uses a return fuel system (meaning the diesel fuel is recycled and returned to the tank) the fuel system can become contaminated with metal particles, and when we are talking about the finite clearances of the parts, metal shavings are a no-no.
There is a procedure to check to see if the HPFP is failed, and VW probably wont make that public.
What causes it? Believe it or not, VW says most are caused by gas being pumped into the fuel tank. The older cars you could drain, refill and bleed the system, and off you go. Now the newer systems are forced to be more efficient and clean, so the system has gotten more complex, which can lead to some expensive repairs.
OP, please don't give up yet, the TDI is a great car!