Not an easy question,
you are assuming that by buying a vice and some materials you can tie all flies you want and need, and maybe you can, but there is a learning curve, normally many years. The average guy doesn't use up all his materials, often buys hundreds of dollars worth to tie a few flies or gives up on it. Then there are those (I'm guilty) who make it part of a lifestyle akin to religion. Tying becomes a zen and so part of life. I tied commercially for years (my sons still says his education was paid for with fur and feathers) it's more of a hobby now with just a few clients. I've seen and taught countless people at many levels of tying, the bulk give up on it for various reasons, lack of dexterity and patience is the most common. I'd say that if you want to tie just to save money you won't. If you want to tie to learn more about trout hatches and the sport itself then it's worth it. What I find odd is people who do not hesitate to lay down hundreds if not thousands of dollars in rods reels wader etc. and refuse to invest a few bucks in the most important piece of equipment you can have that is closest to that elusive trout. They buy cheap offshore flies that often unravel quickly, have no bearing on what is hatching locally and thus support questionable labor laws offshore. Effectively destroying local markets.
So I guess the question is why do you want to tie? If its to save money it will take a long time to realize a return on investment.
For some it is good for the pocketbook for others it's good for the soul.