The Mercedes Navigation is awful in my experience. It will take you on the worst possible way to get to your destination. I use an app that allows me to send trips to my car via bluetooth. It uses Google Maps which I think is the best platform over apply maps or something else. I would go for the apple play if I had the option. Can't help you on the SD card cost....I bought one from Audi some years ago and it was 1500 Euro. I doubt Mercedes will be cheap or offer a great deal on the card. Hope this helps.