I tie all of my own, and tie a lot for others. I don't fish dry flies a lot so I may trade for them once in a while. As posted before it doesn't make a whole lot of sense to purchase 50 dollars in materials for a few flies you will never use.
It adds to the thrill for me. My favorite thing is to take fur and feathers from animals I have harvested and use that for flies. Make a great full circle aspect.
I also like creating patterns on my own. This is probably the most appealing thing about it to me. You can tweak patterns and make your own renditions of popular patterns. These patterns are not seen alot in fly project waters and I found some time is the trout aren't hitting the standard flies, switching to one of these off the wall creations can be effective.
I love learning new patterns and tying with new materials as well. I love hearing that people are having success with my flies, and that keeps me tying for others.
Some guys like to tie, other just want to catch fish. It is all in what you want to get out of it to be honest.
I think I see ospreys point of this post as to try and get people to give it a chance, and see how much other like doing it. You can honestly learn to tie for very cheap. Many guys on here have some older vices and such that they might even donate if asked.
i watched my tying go from a hand-me-down vice to a regal knock off and now a regal with Staninless steel jaws. All of these items are great and help tying go more smoothly, but one can tie on a 5.00 yardsale vice and buy some cheap hooks and steal some fur off of the cat, or even find a turkey feather and create some fish catching patterns.
You will never know everything about tying, and there is always new tricks, skills, and patterns to learn. Plus it is aways fun to talk tying and your own patterns with other tyers.