The “Carte Journalière dégriffé” is the Saver Day Pass, and that you need to buy in advance. Prices do start at 29,- but you have to be really early for that. Look at a date 6 months from now.
A Saver Day Pass is also not refundable.
The “Carte journalière pour le demi-tarif” is always available, always has the same price, and is refundable. So more expensive, but also more flexible, as you can buy it last minute.