Somebody posted this a couple of months ago; I have found it extremely helpful...
City Size: Highest Level Wiz/Sor; GP Limit
Thorp: 1; 25 gp
Implication:
Nothing with a value of over 25 gp will be found here. That pretty much rules out all magic items except possibly 0th-level scrolls.
Hamlet: 2; 100 gp
Implication: You may find potions of cure light wounds and a first-level scroll. Maybe. But that's it. Local hedge wizard can't even make a +1 dagger if he wants to. Heck, he can't even find a masterwork dagger to enchant. Economy might - might - be able to support one minor potion shop.
Village: 3; 150 gp
Implication: Just like a hamlet, there really isn't much to buy here. The local wizard could make a +1 dagger, but there are no MW daggers to be found (cost over 300 gp). Economy might have one minor potion shop and/or scrolls shop but no more. No MW stuff, only 1st-level potions and scrolls. Local hedge wizard can enchant a +1 weapon - but only if you import the MW weapon for him. He won't have the resources to buy one, though.
Small Town: 4; 800 gp
Implications: Town has the resources to support a couple of potion shops, including one that makes "high-powered potions." Might see a 1st-level-spell wand shop. Supports masterwork weapons, but not magic armor, shields, or even minor wondrous items (800 gp is too little). The local hedge wizard can't brew the high-level potions though; he's only level 4. So you're looking at 1st-level wands, 1st- and 2nd- level potions and scrolls, and MW items.
Large Town: 7; 3, 000 gp
Implications: Only in a large town do you even start to see much of a market for items other than potions or scrolls. You will see the occasional +1 weapon or armor and the most minor of wondrous items. Wands might have 2nd-level power. The local wizards may be able to enchant a +2 item for you, but certainly can't buy one from you. Scrolls of 4th level and below will likely be available - but from only one source. Minor potions and scrolls are likely to be plentiful - you might see three or four potion shops.
Small City: 10; 12,000 gp
Implications: You start to see 5th-level scrolls, pretty much any potion is easy to come by, and you may find +1 and +2 weapons/armor - possibly +3 armor, though that taxes the magical resources of the town. Minor wondrous items can be had here. Most wands are probably available, too. There is likely a magic trade, but due to the fact that a typical small city has only between 1 and 4 magicians over 4th level, the trade is probably small and tightly controlled.
Large City: 13; 40,000 gp
Implications: Here, folks have the magical power and money to look at +4 weapons/armor, but they're still rare. You can get your hands on scrolls of 6th and possibly 7th level. Only in large cities do you even start seeing staffs (staves?). Potions are commonplace, as are lower level scrolls - anything you can get in a large town will be easy to find here, though more powerful items will be rarer and limited to a more exclusive group of mages (again, probably less than half a dozen). Also, have you noticed that you really can't even begin to contemplate most RINGS until you're in a large city?!?
Metropolis: 18; 90,000 gp
Implications: Scrolls (any level) and potions can be had here fairly easily. Weapons and armor of all enchantments can be made, but you're unlikely to see a weapon with an effective bonus of more than +6. Only in a metropolis are wondrous items of great power even remotely close to "widely available." However, the magical power is still somewhat consolidated - anything that would be "small and tightly controlled" in a small city is easily found here - lots of 8th and 9th level mages (comparatively) but anything beyond that in power will again be controlled by a few mages - 6 to 8 on average. Considering that metropoli tend to be seats of power, you can bet that at least one of those mages is in an advisory role to the crown (or whatever), which diminishes your chance of finding such items even more.
