If you buy the refill cup it's 1.25 but every refill with it is the same price as a new drink. I think the biggest plastic cup is bigger so it's worth it to me.
But isn't the refill cup the same size as the largest foam cup? All the foam cups regardless of size are the same price, so technically you'd be saving a few cents by just getting the largest foam cup every time you go in.
I'm gonna try looking it up Eh not really finding anything. Maybe next time I go in a store.