How can I move reminders from one list to another by Applescript?
You can't change the container, because this property is read only --> container (list, r/o) : r/o means read only

But you can use the move command

tell application "Reminders"
    set output to ""
    set newList to list "Ausgaben"
    show newList
    repeat with thisReminder in (get reminders in list "Erinnerungen" whose completed is false)
        set nameObj to name of thisReminder
        if (nameObj contains "€" or nameObj contains " Euro ") then
            set output to output &amp; "• " &amp; nameObj
            move thisReminder to newList
        end if
    end repeat
    return output
end tell