I think that depends on the individual Univar Outlet, as I've seen posts about buying Calcium Chloride 77-80 where the hobbyist was told "pallet loads only"
However, I routinely buy individual bags of 20K and 25K (depending on which chemical) from the London Ontario outlet and have been for quite a few years now.
The sodium sulphate I buy costs $14.00 CDN plus taxes of 15%.
If you're in the US where I.O. and other salts are relatively cheap, you won't have a big savings I wouldn't think, but for here in Canada where I am, a pail of I.O. costs $59.99 plus tax for a total of $68.99 and only produces about 140g US mixed to 1.025, for a unit cost of just over 49 cents a US gallon.
My home made mix I just made, works out to just under 9 cents a US gallon mixed to 1.025.
Please remember though, I'm not using this mix in a reef as it is not a complete salt mix, but I use it 50/50 with I.O. in my fish only tanks.
It's great for my brine shrimp and mysid growing operations. (the brine shrimp operation is large, not just for an individual hobbyist)