Congratulations!It's super easy to remove the shell of a Skyriter. There are two screws that connect the typewriter to the base near the back (move the carriage from side to side to see them). Once they're out, the typewriter lifts out of the shell when you simply pull it up and back.
Congratulations on your find! $20 is a good price. Skyriters are really nice to use and fun if you need to work on them. 2 screws and they come out of the hosing. I have several Skyriters and several posts on my blog about them. I also loaded plenty of repair photos to PhotoBucket with more to come as I get time to upload and comment them.
Nice find! 20 USD sounds like a reasonable price. Certainly when it's in good condition, like yours. I don't own a Skyriter myself, but there's plenty of information available on other typospherian blogs.
Too bad I failed to type or should I say spell Skyriter...Ah me. Guess I was too excited....and my name plate has fallen off. Something I have not sorted out yet. For another post.