Many of us started out the game ignoring the Auction House (not really knowing how to use it effectively) and just replacing our crummy gear with marginally better gear as we find it...
While this may work to a certain extent, eventually you're going to start dying a lot and wondering what you can do about it. The key is the Auction House. It's FULL of excellent items at a wide range of prices that you should be taking advantage of.
Don't worry about finding the best or most elite gear and paying millions in Gold until you're level 60 at least. While you're playing through the game you want to hit the Auction House with the goal to find items which are better than your current gear, but won't cost you an arm and a leg. Reason being that as you level up you're gear requirements will change, very quickly too.
Use the refine search options to zone in on what ever specific gear you're looking for, add the minimum mod requirements based on what you're character currently wears. and then sort the listings in reverse order of price. There are plenty of deals to be had below 10,000 Gold which are likely 10 times better then the gear you're wearing. This is one of the bonuses of an open Free Market where prices are constantly changing based on supply and demand.