Is it correct grammar to ask price -how much are they?

No, "How much are they?" is grammatically correct when asking about the price of multiple items. "How much are they?" is a complete sentence, while "ask price" is a phrase that doesn't make sense on its own.

Here are some better ways to ask the price of multiple items:

* How much are these?

* What is the price of these?

* Could you tell me how much they cost?

* How much do these cost?