That was not the cost structure in January of this year, without bundling discount. The cost did not go down from 1 to 2, it went up from 2500 to 3000. Of course, tesla changes pricing all the time so it may not be what it was in january of this year, but I am certain that the cost structure in january for install with no bundle discount is exactly what I posted.
I think the disconnect is, I am quoting just the installation costs as they existed in January. Its possible that what you are looking at is the cost of the gateway + the installation. When I go to configure it on teslas website, it shows "gateway + installation". When I purchased in january the price of the gateway was broken out of the cost of installation as a separate charge.
When I look at just powerwalls on teslas website, the line item for "Gateway + installation" is shown as 4500 for one powerwall, That same line item is shown as 4000 for 2 powerwalls, which fits exactly what was shown in january that 1 powerwall was more expensive to install than 2 (because 1 powerwall always = partial backup, but 2 powerwalls for many people = whole home backup and less install work for tesla).
When I bought, the gateway was 1k itself, then installation. By these charges it looks like the gateway might be more expensive (1500) for the hardware, but they dont show it broken out like they did when I bought. I suspect that the pricing I provided for base installation is still correct, but one could certainly call tesla and get a quote and ask them directly how much basic install is for powerwalls with no incentives.
EDIT: I had to dig a bit at teslas website to get powerwall only quotes. I had to go to tesla.com/powerwall, as that was the only way I could find to get a quote on powerwalls without solar. the basic website navigation doesnt seem to let you get to powerwalls without quoting solar... probably because of the powerwall shortage.