February 24, 2016 by: Dacia Daly35% Off Britax Car Seats Today Only = Marathon Convertible Car Seat $188 Shipped! Today, Feb. 24 only, you can score 35% Off Britax Car Seats – with four different styles to choose from. As one nice example this Britax Marathon G4.1 Convertible Car Seat only $188.49 (reg. $289.99!).