It's true - it costs me about $300/month more in feed alone, not to mention hours spent feeding it. And i could be at a barn that not only fed enough hay, but also had an indoor arena, better footing, a jump course etc etc for $300 more.
The reason I stay is it's the only place within 30 mins of me that has big pastures that arent muddy and herd life, which is for the best for any horse, let alone one who is older. I also really like the atmosphere at the barn, which is more than can be said for many places I've boarded!