Definition from Wiktionary, the free dictionary
Audio (UK) (file)
Usage notes 
- For cost/price, it can be used for both singular and plural, countable or uncountable. E.g., “How much do they cost?” and “What are the prices?” are implied by asking only “How much?”
- For quantity, it is used with uncountable nouns only. The form used with countable nouns is how many.
what is the cost/price