S'mon said:
Yeah, cheap AC boosting items (amulets of nat armour, rings of protection) are a no-brainer. I don't much like Natural Armour as an automatic thing (I never allowed narural armour items in my 1e/2e campaign), I reckon in my new campaign it (1) is rare (druids are rare, wizards don't get Barkskin) and (2) makes your skin look like bark, rhino-hide etc.
The Amulets were slightly more expensive because the Wizardress / Artificer had to get the local Druid to help as well. Course, the PCs had previously helped out the Druid, so he was willing to help (for a small fee

) since the XP for the items was coming from the Wizardress.
Rings of Protection item creation by PCs, however, should be relatively rare at lower level, just due to the fact that Forge Ring is a minimum 12th level caster feat. Very few of the NPCs that PCs at lower levels should meet should be capable of forging them. In fact, very few NPCs should ever have the feat in their lifetimes, regardless of their current level, merely due to the number of item creation feats (and other useful feats) and the greater utility of many of the other item creation feats. So, if you get a Ring of Protection, typically it should be because you find them, not because you have them made for you. Hence, Ring of Protection creation should rarely be an option.
But, I don't understand the DM motivation of making someone's hide look like bark as a deterrent to taking an Amulet of Natural Armor in a game system where balance is decided by a fixed set of character level monetary expectations, modifier possibilities (i.e. different bonuses that stack) and rules on exponential cost increases for a linear increase in magical potency. Even the spell Barkskin does not actually make your skin change appearance (at least in the SRD), it merely toughens your skin.
Why would you want to discourage your players like this?
I can see having the players have to work at either finding a Druid willing to craft items for them and who also has the Craft Wondrous Items feat, or finding a Druid willing to work with some other class NPC who has the Craft Wondrous Item feat who is also willing to craft items for the PCs. That's a roleplaying challenge.
But, I wouldn't change the appearance of the character with such an item. That's a penalty to the PC for no good reason and it automatically gives free information to NPCs about one of the PC's items that they shouldn't have. IMO.