Amazon pricing changes wildly depending on the amount of internal storage you select. My Fire 10 went from $149 to $179 for 32GB to 64GB. Keep in mind that I can get 512GB microSD for about $50-100.
What is interesting about the Fire is that you can decide whether the external storage is in one of two modes. Either as personal storage that can me moved from device to device or as an extension to the internal storage(unconfirmed)
At the moment the Fire 10 has a different set of options from the earlier Fire 7. I’m not certain if the menus are sensitive to the amount of free space or if the features are just different….