You looked at the wrong product. EM-X is not used as a probiotic but as a antioxidant supplement. The phototrophic bacterias have the ability to produce a lot of various antioxidants.
You can extend it to about 20 times its volume by fermenting molasses, although there is a lost in the balance of the microorganisms. Some will tend to dominate others. If you'd make an extension of the extension, some species would probably begin to disappear.
Even if you don't extend, say you take 3 tablespoons a day, it would last 22 days, and you'll be getting a nice dose of antioxidants every tablespoons.
And to quote Jordan Rubin, it's not the quantity but the quality that matters.
So EM is cheap.
Now we just need more people to test it to know how good it really is...