Coffee lovers are a particular group of people. They start thinking about their first cup of coffee before they even go to bed the night before. They are mentally and physically different before they have that first cuppa-Joe in the morning. Drinking coffee can be a social activity, but to many it's a way of life and a means of survival. So, you shouldn't be surprised if they are a little sensitive when you hit them up to buy coffee during your coffee fundraiser.
The problem, then is to show them that the product you are selling as part of your coffee fundraiser is just as good as the specialty coffee they enjoy on a daily basis. You can always hit them from a money standpoint. Raise the point that with the amount of money they have spent on coffee during the last year or so they could have likely had a down payment on a nice home or car instead. This method of convincing may work, but then again - money spent may not matter to a true coffee connoisseur.