I have some experience here. There are varying qualities of flies. (as with everything). Sometimes, the flies fall apart or dries don't float... other times... for 50 cents each, hard to say no. I have found an on line dealer of imported flies & another source that provide flies that are "good enough"... considering how often I lose flies (rocks, trees, bushes, fish)... it's hard to lose $2 a shot... (with $4 per gallon gasoline).
My background is/was "Traditionally Tied Flies"... before JK Hill & all the other companies... until I found a good wholesale resource, quality control was a beyatch...