Travel With Hunny have quietly launched route 848 linking Brentwood with Upminster. It serves stop E on Brentwood High Street and also stops outside the railway station before running through Warley. It terminates at Upminster Station, returning from stop B, just outside Wimpy:
See the route map here and as a pdf here.
Here's the timetable:
...and a list of stops served in each direction:
Please note the 848 only runs on weekdays and is not a TfL route, even though it goes into Greater London, so Oyster is not valid.