The rice flour is used because it freezes without break down, you can use regular flour, especially if you are making it to eat instead of to freeze.

I can get dried mushrooms pretty cheaply at my local warehouse store in a big gallon container, so they are much cheaper than the little 2 ounce packages in the fancy foods or spice section. I whiz them up with some of the liquid from the recipe. Dried "wild" mushroom powder costs about $8 for a one cup jar and one of our natural foods groceries carries it. You could f\try whizzing up a can of mushrooms with a little of the water from the can in a blender and using that for the base, use the rest of the water in the loaf and reduse the salt.