I think Mark means this, a box which provides the front end electronics of an oscilloscope but uses your PC as the display / control panel.
https://www.amazon.co.uk/HANTEK-6022.../dp/B075YPZ44D
Available cheaper in other places, most likely. You can get 'Toy' oscilloscopes for about £20 upwards but for something which will serve you as an essential and versatile electronics tool for this and other projects and repairs you really need to spend a bit more.
If you can borrow a proper scope from somewhere, that's obviously the cheapest option of the lot.