The chicken vs. cow argument goes chickens aren't as valuable as cows, and so you need a way to trade chickens for cows, and so you pay so much per chicken, and pay so much per cow, and now you have a way of trading the two.
However -- this assumes there are people who want chickens, people who want cows, and that the central authority has a relatively fixed pool of money. In reality, that is not how MMOs function. Instead, nobody wants the chickens except NPCs who pay from an infinite pot, in order to remove the chickens from the game. All anyone actually wants are the cows, and so you get infinite and uncontrollable inflation.
To deal with that, you turn the problem on its side. Why are you giving the players chickens, if what they need are cows?
I see this as like boosters in a collectible card game/trading card game. There are only certain cards that have value, the rest are garbage. In order to get the cards that have value, you either buy an ungodly number of boosters or you buy/trade for the card that you want. All the useless cards have no value, at all, and are just filler. Once you have a few thousand basic land cards, you don't really benefit at all from obtaining additional basic land cards. And that is very much how it actually goes.
In the MMO, to remove those useless drops, they use those NPCs with infinite pools of cash. The issue with that is that if someone can afford to buy a lot of boosters, they can generate a lot of cash -- that is, someone who can play all the time can generate infinite cash, and so inflation runs completely out of control.
You deal with that by removing the booster mentality, and instead going to a redemption or ticket approach. When you kill something, rather than drop a rare item randomly, it drops a common item all the time. You trade the common item to a NPC to get a rare item. You have only chickens (stackable), and there's only one place you can trade them for cows. That follows a basic pattern, and allows the players to obtain the items that they want.
So how do you handle crafting, then?
Well, the goal behind the redemption system is to reward based on results -- if I run through a mission in record time, without getting hit, etc. then I get a bigger reward than if I wipe a thousand times It seems like that same logic (to me) applies to crafting -- you don't get the reward from the player asking you to craft the item, the reward -- instead -- comes from the game itself, for doing well at playing it.
This also eliminates the "I'll do that for donations" versus "I want your first born child" problem as well. :)