Some rentals have much cheaper monthly rates (saw Hertz w/ Pontiac G6 at 1,876/month from NY to SF, which is not bad if N>=2). Try to avoid airport pickup/drop off (extra taxes, I think). Check if your CC covers collision, and don't go with the smallest car, since you'll be traveling a lot and want to max your chance of survival.
But you likely know some of this having lived in NY and Oregon (is it?)
Sounds like a fun trip. I've done it twice, but once was a move with a UHaul, dragging my car in tow.