I have just begun to tie my own flies and I don't know the rest of you, but it can be frustrating and time consuming to tie some patterns. I spent about four hours today tying flies and ended up with about a dozen which look good, and about 4 that look like ****. I'm sure that it's my beginner fly tying skills, but 4 flies per hour ain't much more exciting than watching paint dry. Part of that is just me learning the processes of tying and figuring out what I like a fly to look like, of course, and compared to buying them for $2/fly, I do think it was worth it and actually fun when the flies came out looking like they're suppsoed to. I do like to support local outfitters as much as possible, but a lot of the creeks I fish have enough brushy overhang that $2 per fly can mean as much as a $10 loss of investment per trip and I just don't think that flies should cost me that much.
On the other hand, when I want to take a lot of days off work per week to go fly fishing, that can mean that when I have free time at home, fiddling around tying flies often isn't the most productive use of my time. It can be a lot easier to simply find an online store to buy flies cheap. For instance, let's say my time is worth $50 per hour (it isn't), then spending an hour per week tying six flies, maybe I save $11 over buying flies at a local outfitter, but I still come out at negative $39...if you want to look at it that way.
Also, there are many fly patterns that I (and this could be my inexperience tying talking) simply don't want to mess around with, either due to complexity or due to some special material that I don't have. For this, I have found that Blue Fly Cafe
has well tied flies for about $0.70-0.80 each (less expensive if you buy more than 6). I have bought about 40-50 flies from them and one has come apart so far, but I've had flies tied by my local outfitter come apart too (keep in mind this was after fishing with them for a while in both cases). You're probably right in that you get what you pay for, but on the whole I've been pleased with the flies I've bought from them.