There'd be no fee. You pretty much already pay that fee to create your account name (which steemit pays for you).
I'm not sure what you mean by file storage. This isn't hosting, it's just the domain. You'd point your domain at your own server, hosted elsewhere.
You wouldn't be able to transfer a domain without handing over your entire account, since it's linked to your account name. To get around this you might make accounts for a project, like "abcd" would get abcd.steem so you'd make @abcd