Jumping in here (just played catch-up with the entire thread to this point) and one thing that I haven't seen discussed is a Brick and Mortar shop's overhead.
@Tee_Jay I gather from your prior posts that you are in Canada. I am in the U.S. and completely ignorant of all things Canadian; so forgive me any omissions, errors, and non-parallels.
If your initial question is "Is $20/30mL sustainable (read: reasonable)" then you need to look at what costs are actually required to operate a brick-and-mortar storefront.
Real Estate - Buy, lease, purchase viable property that will support/encourage business traffic (Mom's basement doesn't work unless you are talking on-line only... and you were asking about B & M).
Staffing/Personnel -
--Payroll - remember experience, performance, retention, and competion
--Benefits
--worker's comp.
Utilities-
--Gas
--Electric
--Trash
--Sewer
--Communication
Insurance -
--Property
--Theft
--Liability
Inventory - Keeping adequate bulk product on hand that permits you to remain in stock AND accommodate expected future growth.
--Purchasing
--Financing?
--Shipping
Equipment -
--Vessels
--Measuring
--Printing
Other
--Expendables
--Storage
--Packaging
--Waste/Loss
--Advertising
Factor all this in with the $0.012/mL cost of the actual ingredients and
to survive $20/30mL doesn't sound quite so outrageous. Divide that potential profit by the number of competitors in your potential market and it feels downright a bargain. Subtract further those of us who would be potential customers but are too cheap (myself included) and therefore DIY. Now it looks like they are all but giving it away.
Honestly, in my small market (Boise Idaho) I have seen quite a few shops come and go
because they couldn't figure out the magic formula; others have survived, thrived, and even flourished... and now have as many as 8 shops in the immediate region... and they don't make their own "house" juice (to my knowledge).
If you're looking to go into the business; all I can say is "Best wishes." It isn't as easy/cheap as it looks.