The $800 million is a preliminary estimate.
While that is a lot, still not that much compared to some of the regional projects.
The only other regional project that has been fully funded higher than that price is the HRBT.
They're still looking for funding for I-64 High Rise Bridge corridor Phase #2 (over $1 billion), Oak Grove Interchange (rough estimates over $300 million), Bowers Hill Interchange (at least $600 million), I-264 Corridor Improvements (over $2 billion) I-64 widening to Richmond (around $1 billion), I-664 Widening & Third Crossing (over $5 billion), etc.
Then there's other projects that aren't currently on VDOT's radar but are going to become / already are serious bottlenecks in the future and would cost at least $1 billion or more to overhaul. A few that come to mind are VA-168, Downtown Interchange Complex
(I-264 / I-464 / Berkley Bridge / Downtown Tunnel), and US-58.
They are planning on using bonds to accelerate the project and repay them back with toll revenue. There's no way tax dollars would get this project completed.
A whole different corridor, that is getting into some of the Third Crossing segments, such as the I-664 bridge-tunnel expansion and the I-664 highway expansion in Newport News and Hampton.
I-664 was recently added to the proposed HO/T network, so any projects that occur along there will likely include at least one HO/T lane each way.