How to say "Ok, then I take X" after your first choice is not available

Question

Imagine you are in a restaurant and you want to order food, you choose your dish but the waiter says that it is not available today.

In English I would now probably say something like

Ok, then I take curry

What is the natural way of saying this in Japanese? I'm asking about the "Ok, then" part.

As of now, I would probably just say

Hmm えとー カレーをおねがいします.

Answer 1

For casual, which is acceptable as a client I would go with

じゃあ、カレーにします。

If you want to be more polite then

それなら、カレーにします。

じゃあ means : then; well; so; well then
それなら means : if that's the case