Does the bag cost anything?
'Busta' — 'BUS-ta'. Two syllables, stress on first.
At the checkout before the cashier starts scanning. Italy charges for both plastic and biodegradable bags. Bringing your own bag ('borsa della spesa') is the norm.
'Ha un costo' = has a cost = costs something. Simple way to ask. Italy banned free plastic bags in 2011. Biodegradable bags cost 0.02–0.50€. Bringing reusable bags is expected.
Ho portato la borsa mia.
I've brought my own bag.
Stating you have your own bag — saves the cost discussion
Può darmi una busta?
Can you give me a bag?
Requesting a bag directly
Quanto costa la borsa in tessuto?
How much does the fabric bag cost?
Asking about reusable bag sold at the till
The Italian 'borsa della spesa' (shopping bag) culture was strong long before plastic bags were banned. Traditional Italian housewives ('massaie') always carried their own woven basket or net bag ('retina') to the market. The reusable bag is a return to tradition.