Everyone should determine for themselves what their budget is. However, if you can afford to pay for an app that brings value to your work, even if it is a little pricey, then you should. At least that's the philosophy I apply to myself. Creating these tools is a lot of work and ingenuity. The developers deserve to be compensated for their efforts. What's more, I want to ensure that the apps I rely on are here to stay. To use TheBrain for example: that is not a cheap app, but it has been around for over 25 years and is continually being improved. That reliability is worth paying for in my opinion. (I suspect you feel the same way.)