The Selectric typewriters are historically significant. You may know that the IBM Beam Spring switch was designed to resemble the Selectric typewriters in feel. The Model F and the Model M were low-cost alternatives to the Beam Spring.
For $15, if you can get them up and running with a small fix then that would be awesome. I think there are a few sites and videos about Selectric maintenance and repair.
If you really like the caps... you could perhaps get converters to Cherry MX or Alps 3D-printed. Mr Interface did that for fitting Commodore 64 keycaps onto Cherry MX stems. There was a small group project that made complete working Commodore 64 keyboards with Cherry MX switches and N-key rollover.