How much does the coffee cost?
QUAN-to — two syllables, stress on first. 'Qu' is like 'kw'.
Before ordering if you are unsure of prices, or in touristy areas where coffee at the bar can sometimes be priced unusually.
'Quanto costa' (how much does it cost) + the item is the standard price question in Italian. Prices for espresso in Italy are regulated — rarely above €1.50 at the counter even in major cities, except at famous tourist locations.
Quanto viene?
How much does it come to?
More informal — 'viene' (comes to) is used colloquially for prices
Qual è il prezzo al banco?
What is the price at the bar?
Specific about the counter price — clarifies you want the cheaper standing rate
Avete il listino prezzi?
Do you have a price list?
Italian law requires bars to display prices — ask to see it if unsure
Italy has a law ('Codice del Consumo') requiring all bars to display a price list ('listino prezzi'). The price must be listed separately for 'al banco' and 'al tavolo'. Famously, the espresso at the Naples train station bar costs €0.90 — the cheapest in the country.