My bag is from Walmart and cost $49. I don't use it that often, don't carry a cutting mat, and carry an inexpensive Brother mechanical machine for traveling. If bad stuff were to happen to my sewing machine, it wouldn't hurt that much. If you intend to transport your machine frequently, a better quality bag is probably a good investment.
I have also used a small luggage bag with wheels - carry on size or the next size up. It was heavier than the sewing bag, and not as easy to lift into my car, though.That has become more important to me in the last few years.