This was your original mistatement
which implies that no matter what one upgrade cost the other was included in the same price.
The first Google hit for the poor pricing I got was
Tesla announces Model S Ludicrous upgrade, 90-kWh battery but I didn't feel like digging through the other 475,000 results.
what I actually wrote was $8000 or so with there being a significance to the "or so" that you missed. I don't know how much the labor or tax will cost and the first Google result I found said $5000 for one and $3000 for the other. I thought it was clear that "or so" meant it would cost more but apparently I should have used a larger disclaimer.
I didn't bother searching any harder because as this thread and others have shown it is next to impossible to nail down actual costs for upgrades. I figured that horse had been beaten enough and chose to say "or so".
I see now that I left out the punctuation between "or so" and the following fragment, it should have been more like
"Heck if you upgrade the pack from 85 to 90 and get the insane to ludicrous upgrade at the same time spending $8000 or so, they should throw the LTE upgrade in for free."
maybe with the comma in there you would have read the sentence differently? Or maybe anything less than a 4 paragraph disclaimer would have triggered a discussion of how much more installation would cost.