I got this 1951 Smith Corona Silent for what I think is a good price, $33.00 plus shipping. It needed a bit of cleaning and it was missing a couple of things: a right platen knob and a case.
I crafted a substitute right knob from a wine cork and a metal lid from a bottle of ice tea.
The case was a bit more involved. I made it out of coroplast, the kind of corogated plastic commonly used for political signs. I've made a variety of things (bike fenders, panniers, simple boxes, etc.) using just recycled signs and zip-ties, but for this project I bought some things to make a nicer looking case.
From Amazon I got plain black coroplast, coroplast rivets, a latch, and a handle. Various bolts, nuts, and washers I got from my local hardware store. The nylon safety strap I had laying around. For padding, I recycled some packing foam and I made a little pillow (filled with packing foam) from a plastic express mail envelope.
The resulting case keeps the typewriter pretty secure. It probably would have been cheaper to scan eBay for a junky old similar Smith Corona with a workable case, but making this case was a fun project.