This is certainly a reasonable view for a developer/hacker. For other small businesses that want an app that they can rely on, paying a small amount every month

This is certainly a reasonable view for a developer/hacker. For other small businesses that want an app that they can rely on, paying a small amount every month means that they can get support and that the app won't suddenly stop working. It doesn't mean that 37signals price points are correct, but for business related apps free can be the wrong price.