I can't tell you how much money I spent on the leaders in my first year of fly fishing. Over the winter, I read an article somewhere that shared the following trick with me. It's simple and addresses the problem of "using up" your leader.
As a New Fly Guy, I knew that I had to add tippet to the leader and, of course, that tippet would wear down as you tied on new flies. Eventually, it would get down to where the tippet joined the leader via a surgeon's knot. At that time, I would to attach a fresh piece of tippet. This typically caused me to destroy the bottom 4 to 5 inches of the leader to tie the knot. It would not take very long, at the frequency I changed flies and used up tippet, before I had to put on a new leader. In my first season, I was probably getting two or three trips out of a leader, not counting the number of leaders I destroyed with "wind knots" and rock abrasion.
Anyway, the trick is simple. Once you put a new leader onto your fly line, tie a surgeon's loop at the end. Also tie a surgeon's loop at one end of your section of tippet and then make a loop to loop connection with the leader. When your tippet wears down to the loop to loop connection, it's a simple matter to cut it, do a new surgeon's loop, and attach the new tippet to the existing loop on the leader. You never wear down your leader at all! This means that the only reason to change your leader is if it gets all screwed up with wind knots, abrasion or you just don't like it anymore.
As I think back over this season, my second, I do not believe that I use more than 4 leaders spread across several different weights of line. Given gas prices, this ended up being a pretty good deal since the cost of a new leader was equivalent to a gallon of gas in the middle of the summer.
The purists might claim that this will interfere with the turnover and presentation of your fly. The article indicated that this was not a problem and, given my level of skill, I certainly did not perceive any appreciable difference.
Animated instructions on how to tie a Surgeon's Loop