If it is only half the atoms it would stand to reason that half the price would be appropriate. However, if it is half-atoms that might be pricey indeed as those are pretty rare little buggers.
You know, 4000 PPM is 4 grams per liter. That would indeed be a lot of silver. And they even have a 15,000 PPM product. That is roughly the amount of silver in two and half silver quarters. Then again, our poster apparently has particles and parts per million confused. 4000 silver atoms would not be very much silver at all.
Say, I wonder if they use the alien technology like the last great new silver product we saw hyped here? If not, which do you suppose is best - alien technology or single atoms?