This footnote is interesting:
The Design, Development, Test and Evaluation phase of a flight vehicle program typically culminates with development and production of the first vehicle. For the Orion Program, this phase involves the development of two vehicles and will culminate with development and production of the vehicle that will be used for EM-2. The Production and Operations phase covers vehicles produced for subsequent missions and the Capability Enhancements phase, which includes a relatively small amount of reserve funds, makes modifications to those vehicles.
EM-2 is in 2023 and according to this part of DDTE. So the few Orion flights from then to 2030 come at a cost of $7.8bn. Even if there will be one flight per year from 2024 onwards that's $1.1bn per flight. Significantly more than the HEFT unit cost estimate ($840m).