Let's compare our formulas on pure AC eq:
Walls of Jericho -1.3 +3hpr +20flail dam, best ingame -1.2 (hard to get)
real price: 690, by your formula: 100(?), by my formula: 405 (+bonus for difficulty).
an adamantite-plated knight's war robe -0.6
real price: 350, by your formula: 500, by my formula: 405
Well, not too many pure AC items here.
Let's get some dex, con, max_dex, max_con items, because we both can calculate it now.
First of all, helm.
There is an Olthoi Great Helm in eq list -1.5 +3 resfire
real price: 1100, by your formula it should be 750, by my new formula: 405.
The helm gets -0.2 AC and loses max_con. By your formula it's +2*500 -250 = 750 drachmas.
By my new formula, where i count 1 max_con as -0.1 AC, it's 405.
I didn't count -saves in both cases.
So, both our formulas differs from real price a lot here.
Redsteel Legplates of Hades -1.7 +max_con
real price: 600, G-formula: 250, Z-formula: 405
Hiddenite-Encrusted Guards: -0.4 +max_dex
real price: 800, G-formula: 250?, Z-formula: 80
It also looks like the price for -0.5 +max_dex in your formula will be 250 too.
Well, max_dex is special stat, let's ignore it yet.
amethyst-inlaid mithril bracers of the Dwarf Lords -0.8 +max_con
real price: 370, G-formula: 250, Z-formula: 405
a dwarven robe of stoutness/an elven cloak of agility -0.5 +con/dex
real price: 150, G-formula: 200, Z-formula: 195
I'd say my formula replicate the status quo even better than your, while both formulas have some problems and needs to be improved.
Also, it shows some problems with current pricing, i definetely not going to pay 800 drachma for Hiddenite-Encrusted Guards to trade max_con (on my -0.8 +max_con guards) for -0.1 AC.
Just noticed u count -0.1 AC as 500 drachma, not 100, fixed calculations above.
Well, actually, our formulas looks similiar with not too OP items.
With this eq the difference is only at cost of AC/stats.
Your point of AC costs 500, mine 405, your point of max_con costs 250, mine 405.
The real difference will be at ultimate eq, not sure it's even implemented
But i'm pretty sure the price should raise exponentially.