If you are just going to do it as an Internal drink then I think you would be better to get information on cost, After that you would need to get information on your potential volume of users in the office.
Once you have those two things you will then have to figure out why your boss would want to engage in such an endeavor, especially since the users are already buying them on thier own and have their own brand preference.
Unless you are employed by GM, IBM, WalMart, etc. and drinking the company ED would be mandatory I can't see why this would make sense!
Whether you think can or think you can\'t, you\'re probably right!