Magic will break any "realistic" economic model, if only because it isn't "realistic".
Over the different editions we've joked about the simple exploits of the published prices: In one edition iron pots sold for less, per pound, than iron as a trade commodity. In theory you could buy pots and sell iron at a profit indefinitely. In another a 10 foot pole cost more than 1/2 the price of a 10 foot ladder, so people speculated that you could buy ladders, split them into 10 foot poles and make infinite profit there.
But there are other, far different abuses available when magic comes into play. While Teleport can span the globe much faster and more safely than any sailing ship, the cargo capacity is significantly less. Still, there have been spells in different editions that could bypass that problem: Itemize in 2E, Shrink Item in 3e etc. Big cargoes get small and light, and a caster can fit a hold's worth of stuff in his Bag of Holding.
Then we look at what it takes to actually build that ship or cargo wagon, or the quality goods that require a master craftsman to make. And we look at spells like Fabricate, in 3.* and Pathfinder. Same skill levels required, but the days, weeks, months or years needed to craft the item (with all the skill checks that could fail along the way) are reduced to a single skill check and a few minutes time.
Food? Pity the farmer who can't/won't/didn't pay the local Druid to bless his field. Plant Growth (again3.* and Pathfinder) increases crop yield sharply. And, large scale, that makes a huge difference in the economy as a whole.
Through much of the Middle Ages in Europe, something like 95% of the population had to work on farms to grow enough food for everyone. That means that the economy can only afford to have 5% of the people work as craftsmen, merchants, scholars, clergy, and yes nobility. Improvements in farming and crop yield mean that there can be more skilled people other than those on the farm. And that's the foundation of societal wealth. (IRL it's been speculated that the Renaissance can be tied to the introduction of new food crops from the New World, particularly the potato.)
Much of the English wealth that fueled their Renaissance came from a shift to wool production under King Henry VIII, and a policy of religious tolerance under Queen Elizabeth that allowed Jewish scholars, teachers and skilled craftsmen who were fleeing the Spanish Inquisition to come to England and practice their trade there.
So in many ways the "Sheep is Power" quip holds some real world meaning.
Any society that has access to magical transport, such as Gates and Portals (which can take substantial cargo loads) is going to get rich pretty quickly. The Spice trade had a 40,000 percent profit margin, even counting product damaged in shipping and the loss of entire ships to pirates and foul weather. If my country can magically access the far markets for exotic goods my neighbors want, then my neighbors will be better off trading with me than risking their venture capital on a ship that takes months to build and years to sail there and back (if it makes it at all).
It's been said that economists are learned folk who have studied the intricacies of commerce and the human elements of trade, and who (when challenged) will stand together, shoulder to shoulder, and disagree with one another.
Add in such transient and unpredictable elements that Magic can supply and it's even more of a guessing game.
So set your economies up as you will. And yes, leave a few exploitable holes for players to seize upon and abuse. I mean, there are bound to be some anyway, but if you design in a few fairly obvious ones you'll at least know where they're going, and you can decide exactly how big that wormhole can be. (After all, ladder staves are kind of heavy, and there's only so much market for 10 foot poles.)
Besides, if your players think they're getting away with something it makes them feel better, feel clever and special, and it keeps them from digging up exploits that you hadn't considered.
For me, I just use the prices listed in the books, plus or minus a bit based on the location and what I have listed as local product and what's "imported".
