The games will either be $39.99 or $59.99 (Both are too high IMO). Where's this $50 nonsense coming from?
I think you're confusing the 1990s world with the present day world.
Cartridges are cheaper, faster, higher capacity, potentially harder to pirate*, more durable, and more convenient for consumers.
Disks are familiar. Floppy disks were also familiar once.
Also, the base cartridge is rumored to be 32GB and cost $0.05-20. (A BD costs $0.15-30).
The DS's largest 512 MB cartridge was 2^7x the size of the smallest 4 MB cartridge.
The 3DS's largest 8 GB cartridge was 2^6x the smallest 128 MB cartridge. (Never used and discontinued due to 32-bit constraint. Nintendo is bad at planning.)
Assuming a similar pattern for the Switch, we could see a 1-4 TB cartridge Pokemon and Final Fantasy/Dragon Quest/Bravely. Stick that on a flashcart microSD.
* I doubt Nintendo will put in that much engineering effort though.