Its free market, and the prices go down and up depending on certain item aviability/demand - like in real life :). l2 market is pretty interesting stuff. For example ewc price 1,5 month ago was 2,7kk, then it raised to 4kk, and now it is like 3,2kk. My guess would be that lot of players were enchanting stuff at same moment or someone was buying all ewc's and raised prices that way. There is no web to check current prices - best info is shops in gh.
Now 2.0 is comming and prices for some items will change - increase in kesh price(a duals), decrease in ewb, bop, eab - these will be more easy to get. I remember sls price was 3kk on 1.0 or 1.3, and when we got sls*sls duals it went to 20kk~ for single sword.