There are actually free ones.
You can get one by doing a TELNET to sdf.lonestar.org and logging in as "new" - it will prompt you for additional information. After you create the account you can use ssh or telnet to tty.freeshell.org. (They have other servers as well.)
They do make you do a $1 Paypal payment to insure you're a real person or the account will expire. I've had mine for a few years now and have never gotten any request for additional money. I think they do have other options for a larger donation that will give you more capabilities but for my purposes the basic account is sufficient.
Another more complicated one I've used is at Linuxzoo - this essentially creates a virtual account but you wouldn't want to use it for permanent storage: