I am planning to create another app that might generate a similar income stream. I've done 0 paid advertising - only some posts here-and-there; I would probably have more sales if I knew how to market my app better.
https://videohubapp.com/en/ - MIT open source: https://github.com/whyboris/Video-Hub-App
Generally I would say try to minimize the amount your spending per keyword - broader search terms or the broader options on those search terms always cost more.
Might help a ton if you renamed your software to something that is more searchable (or just add some kind of name on the end or start)
For something like this I would probably start at like 30$ a month and keep optimizing - worst case you lose only a few hundred over the course of a year.
But it is almost impossible to get any worthwhile traffic from Adwords in 2022 (in terms of volume or quality) at 5 cents a click.