There is still a cross grade option on the Buy page, but not sure if Sonar is still a valid product, IIRC from threads on GearSlutz and other places it would be, what isn’t on offer is a further reduction on the cross grade price. Also, I think the offer was for Platinum/Professional only.
Best bet is to contact Steinberg or one of their dealers.
One thing to note is that you will need an eLicenser if you don’t already have one.