You want to use the Schleswig Holstein ticket, €29 is for one person, 2 persons are €32. (the currency here is just Euro, not $) The ticket is a day ticket, you can use any regional train and go back and forth as often as you like (no ICE, IC, EC).
On weekdays it‘s only valid after 9AM, all day on weekends.Edited: 3:48 pm, June 10, 2018
Thank you for the info. Much appreciated.
To find trains that you can use, check "local trains" (to the bottom right) when researching your train connection, and only those trains will be displayed.