it's supposed to, it was supposed to

[joham]

I read this sentence in a book about everyday English of American teenagers:

(Amy and Susan are in a clothes shop)

Amy: How much is it?

Susan: It's supposed to be 90 dollars, but it's 65 dollars because it's on sale. I'm getting it.

I thought Susan should say 'It was supposed to be...'. Am I right?

Thank you very much.

[Horsa]

No it's fine it just means that she hasn't bought it yet.