Inscription 1-300 guide is now on wotlk wiki. It's only using druid glyphs as they're the only ones implemented, but the mats for glyphs appear to be set at a uniform 1 ink (3 for higher level) so we can expect it to hold for glyphs for other classes as well. Blizzard may change the cost of glyphs, but it's unlikely that druid glyphs will vary from other same-level glyphs.
The first interesting point is that the amount of herbs you'll need to level inscription to 300 is rougly one and a half of the amount you'd need to level alchemy to 300 (comparison originally by Mortos, who used a random alch power leveling guide for the reference):
7-10 stacks of Alabaster-giving herbs
4-5 stacks of Dusky-giving herbs
3-5 stacks of Golden-giving herbs
4-6 stacks of Emerald-giving herbs
8-12 stacks of Violet-giving herbs
13-19 stacks of Silvery-giving herbs
Vs
60 x Peacebloom , 60 x Silverleaf , 15 x Mageroyal = 6.5 stacks
80 x Briarthorn , 30 x Bruiseweed , 40 x Stranglekelp = 7.5 stacks
30 x Liferoot , 30 x Kingsblood , 5 x Steelbloom = 3 stacks
45 x Goldthorn , 15 x Khadgar's Whisker = 3 stacks
70 x Sungrass , 20 x Arthas' Tears , 40 x Blindweed = 6.5 stacks
40 x Golden Sansam , 40 x Mountain Silversage = 4 stacks
Which gives around 50 stacks for inscription, vs 30 for alchemy (also check out the distributions). This would still place inscription as one of the cheaper crafting professions. It's definitely cheaper then blacksmithing, engineering and jewelcrafting in that level range, and probably still cheaper then all three in the 1-450 range.
The second interesting point is that you produce useful glyphs (for both leveling and endgame) while you level the profession. You can then sell these glyphs, essentially making your leveling free (similar to JC 300-375).
This also means that you'll still need "lowby" herbs well into the endgame. Feral druids are not going to stop wanting that Glyph of Rip, after all. As some old world herbs are notoriously inconveninent to farm, this could have interesting effects on the herb market and the easy availability of certain glyphs.