answers above, all dead on. Can you 'buy' flies on line at half (or less) the price? Without question. Will they be well tied? With little exception.
But what you're trading for a twenty dollar bill is 'Information.' (For Jollies, watch the old TV series "The Prisioner.")
My only toss in is Google Earth'ing the area(s) you want to fish. Amazing what you'll find in the way of 'access' you'd never (or spend hours) looking for "Boots on the ground."
Here in Southern Oregon the current view is 2010 (or 11?) so you're looking at reel time (spelling pun intended). Print photo(s), and off you go. Gather you can do a lat/long cross hairs for your GPS, but haven't figured out how to do that yet (GPS input).