I've been eating Tasty Classics soups for $0.25 per serving, but this is because it was on sale for $0.50 per can. There was a recall of some of the Tasty Classics soup because of possible botulism contamination. I don't know if they'e now stopped making the soup, or if my local grocery store got hold of a large lot of it for almost nothing.
Most canned soup costs $0.50 per serving or more.
I found this interesting post on the Julie At Home blog. It compares the cost of homemade with canned soups.
Based on Julie's comparison, the cost of homemade soup is significantly lower than the cost of canned soup, and the homemade version tastes better as well.
Here is another of Julie's comparisons of homemade vs purchased prepared foods: http://juliemcm.blogspot.com/2010/11/7-foods-you-waste-your-money-on.html