It depends on what you're looking for in terms of type of fly and quality.
There are discount flies that range form $0.50-1.00 a piece for trout flies. These may not be tied very well, have proportions that are a bit out of whack like fat dubbed bodies on dries, or use materials and colors that are a bit odd for the pattern-- they generally are not as well tied as the $1.75-2.00 flies from a local fly shop, or from other online sellers- meaning not as durable, and having a tendency to unravel-- but if --- like many of use -- you're still hanging a lot of flies in trees, or if you are looking for simple flies like buggers and weighted nymphs that there's a tendency to lose on the bottom, or super simple stuff like egg flies, then a discount flies might make more sense. But the quality of the flies you get can vary quite a bit by the pattern, even from the same discount company.
The quality of discount dry flies especially can vary a lot -- you might try a couple generic patterns-- elk hair caddis, adams parachute etc, but generally I've found the quality of flies from cabelas, orvis, and online fly shops (as opposed to discounters), and the flies stocked by fly shops (even though they may have been tied overseas) that sell for $1.75 or so to be much better than the discount flies sold for $0.50 -1.00
Where it makes less sense is when you are looking for flies to match local hatches, like the XYZ hatch on your local river--- in that case you'd be better off getting flies TIED LOCALLY from your fly shop and paying a bit extra.
By the way, if you're looking for a general assortment of trout flies, the Orvis 20 flies for $9.95 promotion deal that pops up in the banner ad on this site, is a very good deal--- well tied flies, and very well known and effective patterns that catch trout all over the world.
And here's another link for discounters:
And then there's the whole issue of fly tying---- you might want to look into that--- though it's no way to actually save money-- but if you're looking for another fun expensive hobby....
Feel free to keep asking questions and good luck