How Big can a 5.2 get?

No; a 2liter jug sells at the rate of 8.96 USgallon, so you can compare it directly to gas. The bottle itself is 3.70C per 2 liter bottle or 1.95C per liter.Smaller quantities out of refrigerated coolers cost way more comparatively, and I only buy by 2liter bottle.
As for milk I buy a 4L jug (3.64USg) at the convenience store for a tic over 8.00C, or about 5.50C to 6.50C at the big box grocery store. These also cost comparatively way more in smaller quantities, and are taxed. Many things we buy are taxed in smaller quantities/ exempt in bulk;the idea being that smaller quantities are a convenience for a well-to-do person, whereas someone buying a jug of it is buying it for his poor family, so deserves a break. Hey I didn't make this system up.
A typical wage for a trained common-tier tradesman or laborer, is about $18 to $20 per hour. So that breaks down to average about 4gallonsImp per hour of average gross wages. But I gotta tell ya, gasoline still seems reasonably priced,when figured this way. In 1969 gas was 37 cents a Canadian gallon and I was making 1.50 per hour minimum wage; this then being 4 gallonsImp per hour's wage. Gas is about the only commodity to have remained like this.
We are lucky to NET 70/75% after income-taxes.
Our combined Provincial and Federal sales taxes is another 13%.
Milk is sales tax exempt in 4L jugs.
Gasoline, Alcohol, and Tobacco are taxed to the extreme.