That add for Dr F&S:
that bottle treats "Over 40,000 gallons" and costs $28.00 or .007 dollars for 10 gallons of treated water. (Call it under a penny per 10 gallons)
Current on line price for Chloramine Buster (not including shipping): One 32 oz bottle treats 16,000 gallons and cost $18.00 or .01125 dollars for 10 gallons of treated water. (This is just over a penny for 10 gallons) or 64,000 gallons can be treated for $60.00 = .009 dollars per 10 gallons, or just under a penny per 10 gallons. (And Chloramine Buster does not smell like Prime)
Aquarium Prime at DrsF&F 20,000 gallons for $45. = .0225 dollars per 10 gallons, or a bit over 2 cents per 10 gallons of treated water.
Pond Prime = .7 cents per 10 gallons
Aquarium Prime = 2.25 cents per 10 gallons
Chloramine buster (quart) = 1.25 cent per 10 gallons
Chloramine Buster (gallon) = .9 cents per 10 gallons
Amquel Plus (gallon) = 4.4 cents per 10 gallons
(All these prices do not include shipping)
Note again the pond sized bottles are good for large volumes of water. If you have just a couple of Nano tanks, you are probably not going to want to pay $50 or $60 dollars for a lifetime supply of dechlor, when you can get Aquarium Prime in smaller (easier to store) bottles. It is still the most cost effective product, even when you get away from the 'large economy' size.
If you want a laugh at how packaging rules look at the tiny bottles for Betta keepers. One of those (priced at Pet Smart) treats only 16 gallons of water and costs $4.00 (that is $2.50 for 10 gallons of treated water! but it also includes a bit of fish food in the package) Another one comes out to 50 cents per 10 gallons (Top Fin Betta Water Conditioner, in a 2 oz bottle treats 60 gallons, costs $3.00) Another is Aqueon Betta Bowl Plus. Dosing is 5 ml per gallon, and comes out to almost $2 per 10 gallons of treated water.