The exact (not Fool's cap) price, at which if you buy any amount of herbs and turn them to enchants, and make 0 profit, is 1g56s25c (maybe little less, because parchment is for 15c). To make same profit with selling herbs on AH, you'll have to sell for 1g64s48c (because AH cut).
So:
if you can sell raw herbs for >1g64s48c, sell on AH.
1g56s25c < mill your own herbs < 1g64s48c
f you can buy herbs for <1g56s25c, buy herbs, mill your herbs, and make enchants.
1 enchant is made from ~12 herbs, each herb takes 0,4sec to mill (milling takes 1 sec for 5 herbs + ~1 sec for looting), making ink from pigments takes 2sec/ink, making enchant takes 3 sec. That's 4,8+6+3=
13,8sec for 12 herbs/1enchant
Let's say my scribe have 4*16bags + 16slot backpack -1 slot for Hearthstone - 1 slot for Virtuoso Ink Set - 5 slots set to be free when taking mail from mailbox= 73 free slots for herbs.
That's 1460 herbs in one round.
Geting 1 stack of herbs from mail - ~ 0,2 sec (i dont know, just a quess) => Filling my inventory takes 15 seconds
traveling between from AH to mail to parchment vendor and back = ~36 secs
waiting for mail to refresh = 45 seconds (1 minute - 15 seconds spent by filling my bags). i won't count that because I may still have herbs in mailbox.
Also traveling may take less, because you still have something in mail and bot will skip AH for next round.
So:
after some counting (processing 1460 herbs take 27 minutes?

), my numbers seems wrong. I dont see where i made mistake and I gave up
Do whatever you want:
for fast money, sell raw herbs.
if you count every silver, and dont care about time. buy herbs and make enchants.
for fast money if you count every silver: buy for less than 1,5g, and make enchants.