Why pay 27USD for 4 oz of ionic silver when you can make it for pennies per oz?
I could see where someone may not have the means to make their own CS at home and where buying a ready made solution could get them out of a bind. - Though I would never recommend paying $27US for 4oz of a 23ppm CS. - that's just wrong
Bottom line is, the nature of the Colloidal Silver manufacturing process will often causes price to rise exponentially. Though what remains outstanding with this is where most solutions will not prove to be more effective than the home-made solutions in practice.
That said, in most cases, the customer will pay for; the facilities and equipment costs, filtering and bottling, packaging, marketing and distribution. O which, far exceeds the initial costs of the product itself.