If software is cheap enough, there’s very little reason not to buy it, if it’s useful to you. The main thing that puts me off at that point isn’t spending the money. It’s the time and effort taken to make the purchase, then enter a serial number and store it somewhere safe for the future.
It’s not really a problem I have with buying, so much a little friction in the process.
That’s what the iTunes store does. It removes that friction. I see an app I like the look of, I tap a button, then tap again to confirm. Moments later, i’m using the app.
That speed and simplicity makes me buy more software. Generally, I’m buying at a low price, but it’s easy, so I do it.