No one can really tell you a definite answer. It fluctuates, even on a single server. On my server, for example, I've seen it range from 12g to 35g depending on:
>> How readily available the materials are
>> How cheaply/expensively those materials are priced
>> How many competing enchanters have been saving up mats
>> The day of the week and time of day
>> The number of farmers logged on at any given time
>> The price of eggs in China
Just look in the AH at the price of what materials would cost, and choose how much you care to mark up the price. Also listen in the Trade channel for how much other people are selling it for and base your pricing from that.
As an aside, Auctioneer will do you no good by itself, as an enchanter. However, EnchantingSell or EnchantingSeller (from www.curse-gaming.com) will use the information from Auctioneer to pick up the cost of mats and combine it (along with a markup) into an estimated cost for each enchant, if you want an addon that will price things for you.
FYI: yes, all of the above factors matter! Heck, the price of eggs might even matter, if it affects the desperation of farmers to get more money and their willingness to sell mats at a lower cost! And more farmers sell for less at certain times to meet quota, also the more people online, the more competition in the AH and on the Trade channel. Enchanting is one of the most confusing trade skills to work with, I tell ya!
Edited, Aug 13th 2006 at 8:20pm EDT by Myxtix