I've found a good way of finding out prices for enchants in game. I use Auctioneer to see the average prices of enchanting regeants I will use for an enchant.
For example, if I have an enchant that uses 4 strange dust that cost, on average, 5s each on the AH, then you can charge 20-25s for the enchant.
This way, you're making the same money you could if you were to sell the regeants.
Another way, is simply to take note of the prices other people charge for their enchants and use their prices. Don't be tempted to sell for cheaper than the regeants are worth. Otherwise, you may lead people to think enchants are cheaper than what they're actually worth, thus making it hard for other enchanters to make money.