You don't have to pay to get up to date info (at least not when I was using it in BC) but it's like wowcensus, and only gets its data from users of their mod uploading data. Unlike auctioneer, wowecon only saves data when an item SELLS and not just what it's listed at. This means that some joker listing 100 stacks of X for 100x the current price won't mess up the data at all (unless someone buys it). The downside is that it only records data if the buyer or selling is running the mod, not any random person scanning the AH.