I'm not familiar with Cellex C. But, are you talking about a c-serum to boost collagen production? If so, you can make your own by using a pharmaceutical grade c powder and mix it with a base of either distilled water or glycerin, 1:4 part ratio. I use water because glycerin is too greasy for my oily skin. You would mix up small batches, ie tablespoons. Keep in a colored glass bottle and refrigerated. It should last a week or two, then make up a new batch. This lessens the chance of the serum oxidizing. It's very cheap in comparison.