There are a few maxi Cosi discounts at the moment on Amazon, this was the best (discount) I could find for an isofix group 123 seat.
Maxi-Cosi Titan Toddler/Child Car Seat Group 1-2-3, Convertible Multi-Stage Forward Facing, Reclining ISOFIX Car Seat, 9 Months - 12 Years, Basic Black
The Maxi-Cosi titan is a multi-stage car seat suitable for babies, toddlers and children. This Maxi-Cosi car seat is first used with a five-point safety harness to fasten the child (group one), before becoming a group 2/3 booster that uses the regular three-point car seatbelt, ready for children from 9 months up to 12 years old. For the ideal comfort and fit, the headrest of this convertible car seat can be adjusted with ease. The ISOFIX connect i on with top tether keeps the seat secure in its place and safely connected to the car. This toddler and child car seat has five recline positions from upright to relaxed sleeping for your little one’s comfort. The toddler cushion of this Isofix car seat also provides extra comfort for your baby.