I've been lvl 300 enchanting for awhile now and have made well over 1000G just from it. I'm sitting at a little over 1100g right now and I spend at LEAST 30-50g a day, sometimes close to 200g. Sometimes it's just buying mats for cheaper than average AH prices, and other times it's for gear. That way I do it is very fair to everyone.
I usually check the averages of the mats required to do the enchants.. and everday I will check the AH for those prices. If I see mats are lower than they usually are, I will usually pick up a few spare. And I usually charge 1-2g over the price of mats depending on the rarity of the enchant.
For example. I know that +7agi/+7sta Gloves sell very well, as do other +agi or +sta enchants. Usually the mats for agi will be Nether essences and +sta requires Dream dust for the mid lvl ones. The average on my server is 3g per Greater Nether Essence, and 4-7g per stack of Dream dust. So if I'm looking at AH and I see a nether essence for 2g buyout, i'll buy it. Then when it's time to turn around and sell an enchant that requires 1 Greater Nether Essence, I will tell them 3.5g-4g and BAM. i just doubled my profits. The reason why I do that is because people ask why it's so expensive, or you get those people that always asks for mats and go buy it themselves and then expect you to get it for free. That way, when they look for mats on AH they see your price is slightly higher than the price of mats and it's only fair to pay a little extra for your services.
Now for the big things like Fiery, Icy, Riding Skill, I usually charge 2-3g + mats for the enchant depending on my mood. +15agi I charge 15-18g + mats.. mainly for the pain of grinding these guys. Everyone says it's easier and hell and whatnot.. and the mobs are fairly easy to solo. It takes a long time if you do that. But the problem is that the area you grind is also filled with Horde grinding for faction to pass the tunnel so you get ganked all the time. It took me 2 weeks about 3-4 hours a day before I reached Honored. It takes 3000 rep points to reach the next lvl, and you have to go up 4 reps in order to reach faction.
Anyway, that's the way I price my enchants. Many people have told me I'm very fair and even some of the cheapest of the enchanters. Another trick is that if they get 2 enchants, I'll take 1g off the total, if they get 3 or more I'll take 1g per enchant discount. I get alot of people coming back asking me enchants and alot of referrals.