For just an ordinary cup of coffee, it might seem like that but hey people are innovative to coffee these days and putting all kinds of stuff. Most coffee shops here in my country are also selling frappe. From that they could at least adjust the price up wherein, it won't be an issue where you pay a fee and get a free coffee. It's not that difficult to be honest, unless you're still doing a startup for coffee shop business though I would advise sticking first to fiat and wait for your business to expand as well as your capital before you put Bitcoin payments as an alternative method of transaction there.