I've purchased in mega bulk from these guys (shack, stop, etc). If I do a 10-12 mile float and I'm nymphing from the boat, There's a good chance you'll lose a pile of flies. Between snags, flies coming undun and fish mangling them, I know I've gone through 15+ flies in a day. If I'm up fishing for 4 days, that's a lot of flies and the local shops are selling them at $2.25 - $2.75 each! I'd go broke buying flies.
I think I've posted somewhere before...... for nymphs and streamers I'll buy from the mass producers. Don't expect the fly to last very long though. For a couple of caddis patterns or attractor flies, they're also OK. If you look at the bodies on the mayfly patterns, the bodies are too thick and represent a much larger insect than you'd expect from that hook size. Bass, bluegills, brookies.....absolutely buy their flies. If you are looking to match a cripple #22 Pseudo, they really don't have something that's an accurate representation so you might have to tie or hit a brick an mortar shop in town.