I started tying my own flies back ten years or so. At the time, I had started fishing the San Juan tailwater in NW New Mexico quite a bit. That section of river flows at a constant 42 F, year round, due to a bottom-draw dam. Given consistent conditions around the year, the bugs hatch and the trout grow at fantastic rates. I learned to throw a two-nymph rig under a strike indicator and split shot and was rewarded with catching many two and three pound trout. The hot flies at the time were a vernille San Juan worm in dull orange (still a must-have for anyone on that river, in my opinion) and the "disco midge". The San Juan worm referred to just above is nothing more than an inch and a quarter of micro-chenille tied to a number 14 nymph hook in two places and brought to a point on the ends. After such a fly is used for a while, the chenille begins to hinge at the tie in points and flops back on itself in the water. At that point, it is useless, as the aquatic worms the lure imitates generally lie straight in the water and the fish won't strike a convoluted worm. These things cost a buck and a half apiece and a decent day's fishing would run through anywhere up to a dozen flies. This situation was not acceptable to a budget flyfisher such as myself. Consequently, I borrowed a vise from my grandad and bought a hundred pack of Mustad no. 14 nymph hooks, a spool of no. 6 red uni-thread, and a package of dull orange micro-chenille - all total about seven dollars, and tied up thirty or forty worms.
A disco midge, although tiny (size 18-24) is also very simple, consisting of an underbody of black or red thread overlain with abutting wraps of clear Flashabou with a thorax of peacock herl or loosely spun dubbing. I learned to tie those pretty quick, too.
Alas, those initial savings have long been consumed in the course of tying many more flies. I took a series of lessons and learned how to tie more complex patterns. All well and good, two and three dollar dry flies could be constructed for pennies. Ninety-nine cent bargain dries could be improved upon, with a little care. Then I got into saltwater fly fishing a bit and had to buy more materials and hooks. A large saltwater fly with eyes can cost well over two bucks just in materials and take half an hour to assemble. The expansion of materials necessary for some of the larger saltwater patterns also led to the over-collection of supplies. I have way too many different colors of bucktail, flash, and synthetic fibers now.
Be that as it may, the economics have subsided into background. While tying will never be an end to itself with me and I'll never name a pattern, it has become an integral and practical part of my fishing. For example, heading up to Alaska for a week's fishing for Coho salmon requires about five dozen flies for the three of us. Since I can tie, a small packet of materials and hooks allows me to knock up a dozen or so of the hot pattern in an evening. I can therefor avoid having to tie an initial batch several times larger than that we carry for the first couple of days. Salmon, strange and wonderful creatures that they are, choose different patterns to strike in different years, perhaps because they aren't seeking to eat? Of course, one really has to wonder what a salmon is looking to do at all, as a fly box for silvers (cohos) looks like box of Christmas ornaments done in poor taste, or as a friend better put it "like sweepings from the dressing room at La Cage".