Welcome.
Can you post a link to the calculator?
I don’t think we see a lot of Buick deals here, period, let alone for a specific model (and a loaner, at that). There might not be a ton of data. Have you tried looking at Buick-specific forums to see if there’s more data there?
If the dealer is being honest w/ the numbers, $900 DAS and $324/mo for what should be a perfectly pleasant ICE SUV seems like a decent deal nowadays.