Anybody has the right to choose by its own preferences, but please, don't say the stock balls are useless, because it isn't so. They are just less "Pro" than others, but if you know then and know your irons, you can easily have good scores with them.
I have the same economical problems, I chose to buy equipment using the Earn Free credits and actively use some of the offers, and now I use almost only stock balls without problems. My score are almost the same with the Callies, obvious that they are better, but the stock balls are NOT the reason of low scores. It's how one plays, not the balls. It's always a question of how one plays. You can use the callies and go over par, while scoring a -15 on best of par 5 with the stock balls.