It can get complicated and you've hit on the basics.
Biggest issue is milk cost. If it's a farmstead variety, meaning they also raise the cattle, that factors in.
Other factors: type of milk source. In order of yield:
Sheep (with by far the lowest yield)
There are cow varieties that give 12-14 gallons a day.
Goats average about one gallon a day.
Sheep1/2 gallon or less a day.
But a gallon of sheep milk yields the most cheese per gallon because it's higher in solids. Nonetheless, you can see why sheep milk aged cheeses can be so expensive.
A general rule: 1 pound of cheese requires 10 pounds (or about 5 quarts) of cow or goat milk and about 6 pounds of sheep milk.
A big drum of Montgomery cheddar weighs 56lbs. That's about 560lbs of milk PER DRUM! It would take entire large herds of sheepto makeone cheese.
Breed to breed especially, the daily yield varies significantly. So if you aren't picky about cow type and just want bulk, you buy anything and homogenize it. Cheap. But if you want a variety of Friesan with Higher fat content per yield, and you want single source, and organic, and raw... Much more expensive.
Then there's fat molecules... Protein content... It matters depending on the cheese you want to make. And fat makeup affects total yield, again affecting your end yield. A harder goat cheese might use Saanen goats, if you want a softer cheese, you might use Nubian goats. Different pices from region to region.
If it is aged, especially for longer periods, that also adds up. A fresh new cheddar might sell to n finer for $6-8 a pound. But if the affinity ges it for 18 months, that might double or triple the retail price. And for retail, most monsters want to sell at 2x retail. 2.5-3 is aspirational. Sometimes you see 1.5x but then they might be breaking even.
And as always, small artisan yields don't get he efficiency of bulk production.
Edited by Cary Grant - 7/31/12 at 7:38pm