I am pretty sure the unlimited soda program is $5 per day (someone correct me if I am wrong) so, $15 for 3 day, $20 for 4 day, and $35 for 7 day. If you purchase the mug it would be an extra $5, so if you were doing the 7 day and wanted unlimited soda and a mug it would be $40.
They had a stand right by the elevators on deck 3 when we boarded, but I think someone posted once that you can also get these at any bar on ship.
LeiLani