Mid last year I ran into an issue when trying to interface a PC Sound card to a two-way radio for data comms. I needed to trace and measure audio but ran into a small problem:
It turns out I have never owned an oscilloscope as the places I have worked have always had one - however that is no longer true.

I ended up getting something similar to this from eBay:
https://www.ebay.com.au/itm/Assemble...item4432085e2b It was about $30 assembled and delivered. A build it yourself version is available for less.

It might be a nice, relatively cheap option to add to the project.