Per our conversation...

Yesterday at Picnic at the Park, we were discussing cream soups, because it's case lot sale month and everyone wants to stock up. I mentioned I have greatly reduced my canned cream soup use by making my own mix of flour and milk. Here is a recipe I found in the fabulous compilation book, The Complete Tightwad Gazette, by Amy Daczyczn. (This specific recipe isn't one I have made, per se, although I have used the basic premise frequently. The book is highly recommended.)

Cream Soup Mix

2 c. dry milk
1-1/4 c. cornstarch OR 2-1/2 c. flour
1/4 c. chicken bouillon
2 Tbsp. dried onion flakes
1/2 tsp. pepper
1 tsp. thyme (opt.)
1 tsp. basil (opt.)

Mix all ingredients and store in airtight container. If using cornstarch mix, add 1/3 c. mix to 1-1/4 c. water. If using flour mix, add 1/2 c. mix to 1-1/4 c. water. This makes concentrated casserole consistency. For soup consistency, double the water.

If you have a lot of milk, like we do (yea, cow!) you can just put milk in the blender with the flour or cornstarch and use that.

Not only is this soup healthier (especially if you use raw milk for a base, and a good quality chicken bouillon), it is significantly cheaper.
Store brand soup - 69 cents for a 10 oz. can
Homemade soup mix- Recipe makes ten 12 oz. batches at 18 cents each.

You could also get dried mushrooms at the store, and if you wanted a cream of mushroom concentrate, I would just throw some dried mushrooms in a chopper and add to the dry ingredients, or add mushrooms to the other part of your recipe.

For comparison, here is the list of ingredients from a can of Western Family Cream of Mushroom condensed soup: Water, mushrooms, wheat flour, soybean oil, salt, cream, monosodium glutamate, whey powder, soy protein concentrate, modified corn starch, autolyzed yeast extract, disodium phosphate, maltodextrin, spice, garlic powder, natural flavors (contains milk), dried mushrooms, partially hydrogenated soybean and cottonseed oils.