I know that when creating items that have continuous spell effects you are supposed to look at existing examples to price them, but should special requirements reduce the cost as well? And what's a good way to decide how much to reduce the cost by?
The example that came up was making a ring of nereid's grace (bonus to AC equal to Cha as long as you don't wear armor, Max +5).
A ring of protection +5 costs 50,000 so that's a good starting point, but it doesn't depend on Charisma and it works with armor (nereid's grace doesn't).
Making a ring of nereid's grace based purely on formula ends up half the price to get up to +5 (specifically 24,000).
What's a good price for this item?
Edit Both rings provide the same deflection bonus to armor Edit