This sensor you refer too is the one of the feed line to the HPFP right? If so, yea... I would replace it while the intake manifold is off. I'vee lots of guys say this sensor goes bad. Most dealers even seem to want to do a COD(ie you pay!) repair while replacing the HPFP under the extended warranty('08's thru '10's N54's).
Has your HPFP been replaced before? Maybe this sensor has been replaced and can be replaced again? (under a parts warranty). IF it was replaced as part of a HPFP, BMW would foot the entire bill. ~$84 doesn't sound bad for the sensor though. I would just replace it yourself or have the shop that is doing your walnut blasting.
G.L.
Dack