I don't know...I think I can make 1/4 year supply for less than one of those bottles of the store-bought stuff.
Baking soda: couple of bucks
Epsom Salts: couple of bucks
Ca: $17 from BRS (and it's a gallon's worth...which will probably last me the rest of my life.)
So, maybe $10 or so for a 1/4 year supply on a 60g SPS dominate system.