I don't know why I hadn't started doing this sooner. It was probably out of convenience. On sale I can get Spaghetti Sauce for $0.99. On sale I can get plain tomato sauce for way cheaper. So, now I buy the plain sauce and add my own chopped onions, green pepper, italian seasoning, basil, and some garlic powder. This way I am getting it my way and it tastes better. It's very versatile. You can add pretty much anything you want to this sauce; mushrooms, chunks of tomato, other veggies, etc.
This summer I am growing Roma tomatoes and I plan on making up tons of sauce to freeze and can.