A single, non-discounted, one-way train ride between the two biggest cities, Amsterdam and Rotterdam, costs €20,20.

The promotional price of this subscription is only a few euros more expensive than the existing unlimited subscription for weekend train travel (i.e. 6:30 PM Friday to 4:00 AM Monday), which costs €39,50. You can pay €4 extra for a 40% discount the rest of the off-peak hours.

With that discount, my commute (Haarlem <=> Amsterdam) costs €3,30 each way. A single trip to work a month makes the promotional subscription better value.