you can compare all the options.
There are no week-cards, which I've always thought was a pity.
So the steps are: day-cards bought individually, day-cards bought in a multipack as explained above, then the next jump is a month-card, then a year-card.
I guess it depends how long you're going to be living here and doing this commute. In some cases, a year-card is so very much cheaper than 12x a month-card, that being away for a few weeks, now and again, still makes it worth it.