Yes agreed very much cheaper! I got mine online for less than $400 delivered and have a buddy who's licensed and can do the install. So yes much cheaper than the 12k plus for the Sunrun HIS install ;)
I just called them because I had the same (no powerwall just Solar) and they claimed their IT system was spitting out incorrect quote numbers and they were working to fix it.
8k is not an overreaction... it might be too low. All in for HIS at my place I am looking at over 12k at Sunrun prices. Yes you can cut that down some but its expensive, it's gated by Sunrun currently, and it's overkill.