You can purchase from Ebay,- small open board type, battery operated or power supply operated small COMPLETE new oscilloscope, for under $30. It's digital from China, and gives readings in volts, frequency, duty cycle, shows waveform, etc. It comes with probe, but 9v DC 1 amp PS has to be purchased extra if desired. Be careful to get the soldered-welded one, not the kit of parts. DSO 138 Comes with instructions manual sheets use and complete schematic. Get locally, - a plastic school pencils box to keep it in. I have (2) and they work fine.

 

There are quite a few differences in performance of the oscilloscpes described in post #21 and those scopes selling for a few thousand dollars. Frequency response, resolution, and accuracy come to mind as some of the differences.

Clearly, the capabilities required of an oscilloscope depend on the application.

 

Having more than one scope can be Real handy, depending on the project.
I now have a 2Ch Tek and a 4Ch Rigol, but I really could have used them both 10+ years ago, when I had neither.