To get started I over spent on ink. I needed it to help me level in places and to get my glyph machine off the ground. I was paying up to 2.4G an ink off the AH. That put my glyphs at 5.3G each and I sold them for 6G or more. Slim profit but it got me started.
All the gold I earned was getting put back into mats. I started to look at herbs to meet my growing needs. Tigger Lilly was the cheapest I could find at 14G a stack the day I was looking. I never tracked it, but it felt like I got 4-5 inks per stack. But now I was able to produce a lot more glyphs as the inks were scarce on the ah at a reasonable price. Doing the math, it felt like I was over paying for my needs. I just banked the snowfalls and figured that would make a difference.
I later found a spreadsheet that took into account the value of snowfall inks when buying herbs. I recall reading something about that before but now the numbers were looking at me. The more expensive herbs produced snowfall ink more often. That put the milled value per gold huch higer on those herbs. I switched to adder's tongues at 24G and have purchsed very few of those others. I was able to unload stacks of snowfalls during the darkmoon event for 18-20G each. (I could have done cards but didn't feel like dealing with them.)
So if I can get herbs at 24G and sell the inks at 20G, I am only paying 4G for the ink. If I only get 4 inks, that 1G an ink and my glyph cost is 2.5G each. I know some glyphs only take one ink and they don't all take the expensive parchment. I am confortable thinking of each glyph as 2 inks + .5g and knowing that I have some hidden profit in there.
I went from 5.3G glyphs to 2.5G glyphs by taking full advantage of my milling. My next step is to contract a farmer to send me the herbs. If he can sell direct to me he gets to bypass the AH and saves the 5% AH cut. I am over stocked on herbs at the moment or I would have already made that happen. I already see one farmer that I constantly buy out his entire stock.