Agreed. I think Sport will be slightly under $40K and Performance will be slightly under $45K.
No idea on the cost of Nismo without knowing specs. Nissan might decide that's where they want to go all out (carbon fiber, 500hp, GT-R brakes) and price it accordingly.
I think it's too early to decide what the price of a Nismo would be. We already know this was a budget/parts bin car to begin with and even thinking about a Nismo about this point seems almost far fetched. The one good thing about a Nismo variant would be the ability to get more power out of a turbo'd engine than NA VQs.