Nintendo will probably sell microSD cards for the switch at their online store sooner or later. You can get the regular sized SD card there for $11 for 16GB, which don't seem like highway robbery.
https://store.nintendo.com/ng3/browse/productDetailColorSizePicker.jsp?productId=prod10072
https://store.nintendo.com/ng3/browse/productDetailColorSizePicker.jsp?productId=prod10072