I keep on hand a Base salt, Calnit, Epsom, soluble micros, pH down, and potassium silicate.
I'm running Jacks right now, but I'll buy whatever is the best deal in 25# and 50# bags. I rebag the larger bags into gallons then put those in sealed 5 gallon buckets. Then make stock solutions as needed, I think $.02-$.03 per gallon is average cost.
I've not found much difference in the offerings from Haifa, Jacks, Growmore, ICL, Masterblend, Yara and Southern AG.
I haven't tried Megacrop, a lot of people report it leaves a scummy rez.
Silica I use GH Armour Si or Agsil16H both are a good value.
Micros I get 2-4 pound pails from Miller, Growmore, Jacks or ICL.