Of course, costs are relevant for most of us. Air stash is $120 plus cost of SD cards (max storage 32 GB. Goflex Satellite about $200 for 500 GB, and Airstash $250 for 500 GB. All are local options with their own pluses and minuses. Effectively, you are creating your own local cloud. You can also use a home wireless network this way. All will support streaming rates consistent with HD (1018p) video and lossless files (ALAC or FLAC audio). All are entirely under your control, and you do not have to worry about privacy or content.
Moving to someone else's cloud (Apple, Amazon,....) gives you more location flexibility at the potential price of privacy and control. HD files face Space and streaming rate limitations as well as cost limitations when traveling. Note that data rates over cellular connections for roaming from US can be on the order of $20 per megabyte.
Given that Apple has decided for us that we don't need more than 64 GB internally, it would have been nice if they had made it easier to connect external storage.
At least there are some workarounds...
Don't hold your breath waiting for a change.
J