He's talking about the high pressure sensor that's actually attached to the HPFP itself. There's two on there, a low pressure (the one on top) and a high pressure one (commonly referred to as the thrust sensor). Usually when you install a new HPFP you install a new one of those too. It just unscrews and you screw a new one on.
I'm pretty pleasantly surprised how dead on my diagnoses was. Although I'm not happy for the OP because I've been in this situation and it sucks balls.
OP, you can fix this yourself. It's literally T30 torx bolts, 2 electrical connectors, a hose clamp and a 17mm wrench to remove the high pressure line from the OEM HPFP. If you've checked a cam follower you can do this repair. If not, then look up some DIY's on how to do it.
You'll need to replace the fuel pump which is roughly $300 and the thrust sensor which is around $50 if I recall correctly. You can get both off ECS or even cheaper if you search around. For the thrust sensor, when you get the new HPFP you'll see that it just screws into it. There will be a threaded hole for it right on the HPFP. You may have to take some hardware off your old HPFP but other than that, you're all set. It's really not that hard of a job to do.
Best of luck, I know how much of a pain in the ass all this HPFP nonsense can be.