If you were to pay full freight ($85.00) for 5gal of soda ash at bulk reef supply, by my calculations, it would cost you about $0.11 per day to dose 200ml and would last 757 days. This does not take into account shipping.
I have no idea how much everyone is dosing but it seems to me that there is not a lot of margin for savings here...
If the market is so large, why not just do a huge group buy of 5gal pails, have them shipped to port huron for free, pick them up pay some taxes and them resell here? Hell you could even offer refills to ppl who have 1 gallon jugs. If a local store did this the margins would be the savings in shipping and convenience of getting it at LFS with satisfaction of knowing it is the same stuff you have always been using plus it supports the LFS.
Or maybe im way off base, which is usually the case.