Maybe more than in the UK, but here in a supermarket that would be 0.20€ of ham, 0.10€ of chese and 0.30€ of bread. Considering the volume starbucks has, I don’t think it’s unreasonable they would pay half of what you pay in a supermarket.
Of course these numbers I’m all taking our of my ass, but I think they are a close estimate. There’s a reason if Starbucks is so profitable